# 02 - 6A00 Disorders of intellectual development

# 6A00 Disorders of intellectual development

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
In addition, three categories from the grouping of primary tics and tic disorders in Chapter 8 on 
diseases of the nervous system are cross-listed here, with diagnostic guidance provided, because 
of their high co-occurrence and familial association with neurodevelopmental disorders. 
These include:
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Tourette syndrome
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Chronic motor tic disorder
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Chronic phonic tic disorder
General cultural considerations for neurodevelopmental disorders
• The evaluation of the essential features of most of the disorders in this section either 
depends on or is informed by standardized assessments. The cultural appropriateness of 
tests and norms used to assess intellectual, motor, language or social abilities should be 
considered for each individual. Test performance may be affected by cultural biases (e.g. 
reference in test items to terminology or objects not common to a culture) and limitations 
of translation. Language proficiency must also be considered when interpreting test results. 
Where appropriately normed and standardized tests are not available, assessment of the 
essential features of these disorders requires greater reliance on clinical judgement based 
on appropriate evidence and assessment.
Disorders of intellectual development
Essential (required) features
• The presence of significant limitations in intellectual functioning across various domains 
such as perceptual reasoning, working memory, processing speed and verbal comprehension 
is required for diagnosis. There is often substantial variability in the extent to which any 
of these domains are affected in an individual. Whenever possible, performance should be 
measured using appropriately normed, standardized tests of intellectual functioning and 
found to be approximately 2 or more standard deviations below the mean (i.e. approximately 
less than the 2.3rd percentile). In situations where appropriately normed and standardized 
tests are not available, assessment of intellectual functioning requires greater reliance on 
clinical judgement based on appropriate evidence and assessment, which may include the 
use of behavioural indicators of intellectual functioning (see Table 6.1, p. 101).
• The presence of significant limitations in adaptive behaviour, which refers to the set of 
conceptual, social and practical skills that have been learned and are performed by people in 
their everyday lives, is an essential component. Conceptual skills are those that involve the 
application of knowledge (e.g. reading, writing, calculating, solving problems and making 
decisions) and communication; social skills include managing interpersonal interactions 
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and relationships, social responsibility, following rules and obeying laws, and avoiding 
victimization; and practical skills are involved in areas such as self-care, health and safety, 
occupational skills, recreation, use of money, mobility and transportation, as well as use 
of home appliances and technological devices. Expectations of adaptive functioning 
may change in response to environmental demands that change with age. Whenever 
possible, performance should be measured with appropriately normed, standardized tests 
of adaptive behaviour and the total score found to be approximately 2 or more standard 
deviations below the mean (i.e. approximately less than the 2.3rd percentile). In situations 
where appropriately normed and standardized tests are not available, assessment of 
adaptive behaviour functioning requires greater reliance on clinical judgement based on 
appropriate assessment, which may include the use of behavioural indicators of adaptive 
behaviour skills (see Tables 6.2–6.4, pp. 104–111).
• Onset occurs during the developmental period. Among adults with disorders of intellectual 
development who come to clinical attention without a previous diagnosis, it is possible to 
establish developmental onset through the person’s history (retrospective diagnosis).
Severity specifiers
The severity of a disorder of intellectual development is determined by considering both the 
individual’s level of intellectual ability and level of adaptive behaviour, ideally assessed using 
appropriately normed, individually administered standardized tests. Where appropriately 
normed and standardized tests are not available, assessment of intellectual functioning and 
adaptive behaviour requires greater reliance on clinical judgement based on appropriate evidence 
and assessment, which may include the use of behavioural indicators of intellectual and adaptive 
functioning provided in Tables 6.1–6.4.
Generally, the level of severity should be assigned on the basis of the level at which the majority 
of the individual’s intellectual ability and adaptive behaviour skills across all three domains – 
conceptual, social and practical skills – fall. For example, if intellectual functioning and two of 
three adaptive behaviour domains are determined to be 3–4 standard deviations below the mean, 
moderate disorder of intellectual development would be the most appropriate diagnosis. However, 
this formulation may vary according to the nature and purpose of the assessment, as well as the 
importance of the behaviour in question in relation to the individual’s overall functioning.
Disorder of intellectual development, mild
• In mild disorder of intellectual development, intellectual functioning and adaptive behaviour 
are found to be approximately 2–3 standard deviations below the mean (approximately 
0.1–2.3 percentile), based on appropriately normed, individually administered standardized 
tests. Where standardized tests are not available, assessment of intellectual functioning and 
adaptive behaviour requires greater reliance on clinical judgement, which may include 
the use of behavioural indicators provided in Tables 6.1–6.4. People with mild disorder of 
intellectual development often exhibit difficulties in the acquisition and comprehension of 
complex language concepts and academic skills. Most master basic self-care, domestic and 
practical activities. Affected people can generally achieve relatively independent living and 
employment as adults, but may require appropriate support.
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Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Disorder of intellectual development, moderate
• In moderate disorder of intellectual development, intellectual functioning and adaptive 
behaviour are found to be approximately 3–4 standard deviations below the mean 
(approximately 0.003–0.1 percentile), based on appropriately normed, individually 
administered standardized tests. Where standardized tests are not available, assessment 
of intellectual functioning and adaptive behaviour requires greater reliance on clinical 
judgement, which may include the use of behavioural indicators provided in Tables 
6.1–6.4. Language and capacity for acquisition of academic skills of people affected by 
moderate disorder of intellectual development vary but are generally limited to basic skills. 
Some may master basic self-care, domestic and practical activities. Most affected people 
require considerable and consistent support in order to achieve independent living and 
employment as adults.
Disorder of intellectual development, severe
• In severe disorder of intellectual development, intellectual functioning and adaptive 
behaviour are found to be approximately 4 or more standard deviations below the 
mean (less than approximately the 0.003rd percentile), based on appropriately normed, 
individually administered standardized tests. Where standardized tests are not available, 
assessment of intellectual functioning and adaptive behaviour requires greater reliance 
on clinical judgement, which may include the use of behavioural indicators provided 
in Tables 6.1–6.4. People affected by severe disorder of intellectual development exhibit 
very limited language and capacity for acquisition of academic skills. They may also have 
motor impairments and typically require daily support in a supervised environment for 
adequate care, but may acquire basic self-care skills with intensive training. Severe and 
profound disorders of intellectual development are differentiated exclusively on the basis 
of adaptive behaviour differences because existing standardized tests of intelligence cannot 
reliably or validly distinguish among individuals with intellectual functioning below the 
0.003rd percentile.
Disorder of intellectual development, profound
• In profound disorder of intellectual development, intellectual functioning and adaptive 
behaviour are found to be approximately 4 or more standard deviations below the mean 
(approximately less than the 0.003rd percentile), based on individually administered 
appropriately normed, standardized tests. Where standardized tests are not available, 
assessment of intellectual functioning and adaptive behaviour requires greater reliance on 
clinical judgement, which may include the use of behavioural indicators provided in Tables 
6.1–6.4. People affected by profound disorder of intellectual development possess very 
limited communication abilities and capacity for acquisition of academic skills is restricted 
to basic concrete skills. They may also have co-occurring motor and sensory impairments 
and typically require daily support in a supervised environment for adequate care. Severe 
and profound disorders of intellectual development are differentiated exclusively on the 
basis of adaptive behaviour differences because existing standardized tests of intelligence 
cannot reliably or validly distinguish among individuals with intellectual functioning 
below the 0.003rd percentile.
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Disorder of intellectual development, provisional
• Provisional disorder of intellectual development is assigned when there is evidence of a 
disorder of intellectual development but the individual is an infant or child under the age 
of 4 years, making it difficult to ascertain whether the observed impairments represent 
a transient delay. Provisional disorder of intellectual development in this context is 
sometimes referred to as “global developmental delay”. The diagnosis can also be assigned 
in individuals 4 years of age or older when evidence is suggestive of a disorder of intellectual 
development but it is not possible to conduct a valid assessment of intellectual functioning 
and adaptive behaviour because of sensory or physical impairments (e.g. blindness, prelingual deafness), motor or communication impairments, severe problem behaviours, or 
symptoms of another mental, behavioural or neurodevelopmental disorder that interfere 
with assessment.
Disorder of intellectual development, unspecified
Additional clinical features
• No single physical feature or personality type is common to all individuals with disorders 
of intellectual development, although specific etiological groups may have common 
physical characteristics.
• Disorders of intellectual development are associated with a high rate of co-occurring 
mental, behavioural and neurodevelopmental disorders. However, clinical presentations 
may vary depending on the individual’s age, level of severity of the disorder of intellectual 
development, communication skills and symptom complexity. Some disorders – such 
as autism spectrum disorder, depressive disorders, bipolar and related disorders, 
schizophrenia, dementia and attention deficit hyperactivity disorder – occur more 
commonly among individuals with disorders of intellectual development than in the 
general population. Individuals with a co-occurring disorder of intellectual development 
and other mental, behavioural and neurodevelopmental disorders are at similar risk of 
suicide as individuals with mental disorders who do not have a co-occurring disorder of 
intellectual development.
• Problem or challenging behaviours such as aggression, self-injurious behaviour, attentionseeking behaviour, oppositional defiant behaviour and sexually inappropriate behaviour 
are more frequent among those with disorders of intellectual development than in the 
general population.
• Many individuals with disorders of intellectual development are more gullible and naive, 
easier to deceive, and more prone to acquiescence and confabulation than people in the 
general population. This can lead to various consequences, including greater likelihood 
of victimization, becoming involved in criminal activities and providing inaccurate 
statements to law enforcement.
• Significant life changes and traumatic experiences can be particularly difficult for a person 
with a disorder of intellectual development. Whereas the timing and type of life transitions 
vary across societies, it is generally the case that individuals with disorders of intellectual 
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Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
development need additional support adapting to changes in routine, structure, or 
educational or living arrangements.
• Many medical conditions can cause disorders of intellectual development and are, in turn, 
associated with specific additional medical problems. A variety of prenatal (e.g. exposure 
to toxic substances or harmful medications), perinatal (e.g. labour and delivery problems) 
and postnatal (e.g. infectious encephalopathies) factors may contribute to the development 
of disorders of intellectual development, and multiple etiologies may interact. Early 
diagnosis of the etiology of a disorder of intellectual development, when possible, can 
assist in the prevention and management of related medical problems (e.g. frequent thyroid 
disease screening is recommended for individuals with Down syndrome). If the etiology of 
a disorder of intellectual development in a particular individual has been established, the 
diagnosis corresponding to that etiology should also be assigned.
• Individuals with disorders of intellectual development are at greater risk of a variety of 
health (e.g. epilepsy) and social (e.g. poverty) problems across the lifespan.
Boundary with normality (threshold)
• In disorders of intellectual development, a measure of intelligence quotient (IQ) is not 
an isolated diagnostic requirement to distinguish disorder from normality, but should be 
considered a proxy measure of the “significant limitations in intellectual functioning” that 
partially characterize disorders of intellectual development. IQ scores may vary as a result 
of the technical properties of the specific test being used, the testing conditions and a 
variety of other variables, and also can vary substantially over the individual’s development 
and life-course. The diagnosis of disorders of intellectual development should not be 
made solely based on IQ scores but must also include a comprehensive evaluation of 
adaptive behaviour.
• Scores on individually administered standardized tests of intellectual and adaptive 
functioning may vary considerably over the course of an individual’s development, and it 
is quite possible that, during the developmental period, a child may meet the diagnostic 
requirements of disorders of intellectual development on one occasion but not another. 
Multiple testing on different occasions during the developmental trajectory is necessary to 
establish a reliable estimate of functioning.
• Special care should be taken in differentiating disorders of intellectual development 
from normality when evaluating people with communication, sensory or motor 
impairments; those exhibiting behavioural disturbances; immigrants; people with low 
literacy levels; people with mental disorders; people undergoing medical treatments 
(e.g. pharmacotherapy); and people who have experienced severe social or sensory 
deprivation. If not adequately addressed during the evaluation, these factors may reduce 
the validity of scores obtained on standardized or behavioural measures of intellectual and 
adaptive functioning. For example, the reliable use of standardized measures of intellectual 
functioning and adaptive behaviour may pose particular challenges among individuals 
with motor coordination and communication impairments, and assessments must be 
selected that are appropriate to the individual’s capacities.
• What is sometimes termed “borderline intellectual functioning”, defined as intellectual 
functioning between approximately 1 and 2 standard deviations below the mean, is not a 
diagnosable disorder. Nonetheless, such individuals may present many needs for support and 
interventions that are similar to those of people with disorders of intellectual development.
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Course features
• Disorders of intellectual development are lifespan conditions that typically manifest during 
early childhood and require consideration of developmental phases and life transitions 
whereby periods of relatively greater need may alternate with those where less support 
may be necessary.
• Disorders of intellectual development may show individual as well as etiology-specific 
variation in developmental trajectories (i.e. periods of relative decline or amelioration in 
functioning). Intellectual functioning and adaptive behaviour can vary substantially across 
the lifespan. Results from a single assessment, particularly those obtained during early 
childhood, may be of limited predictive use, as later functioning will be influenced by the 
level and type of interventions and support provided.
• People with disorders of intellectual development typically need exceptional support 
throughout the lifespan, although the types and intensities of required support often change 
over time depending on age, development, environmental factors and life circumstances. 
Most people with disorders of intellectual development continue to acquire skills and 
competencies over time. Providing interventions and support – including education – 
assists with this process and, if provided during the developmental period, may result in 
lower support needs in adulthood.
Developmental presentations
• There is wide variability in the developmental presentation and developmental trajectories 
of individuals with disorders of intellectual development. Tables 6.2–6.4 provide clinicians 
with some of the key areas of strengths and weaknesses typically observed at different time 
points across development (i.e. early childhood, childhood, adolescence and adulthood) in 
individuals with disorders of intellectual development.
• Conditions related to disorders of intellectual development may be suspected during the 
first days and months of life due to the presence of certain physical signs such as facial 
dimorphisms, congenital malformation, micro- or macrocephalia, low weight, hypotonia, 
physical growth retardation, metabolic problems and failure to thrive, among others.
• In older children, disorders of intellectual development may manifest as problems in 
acquiring academic knowledge and abilities such as reading, writing and arithmetic. Many 
children with mild disorder of intellectual development may not be referred for evaluation 
until they reach school age. Some individuals may remain undiagnosed until much later, 
during adolescence or adulthood.
• The manifestations of disorders of intellectual development during late adolescence and the 
first years of adulthood may be strongly influenced by the presence of challenges related to 
assuming adult roles, such as postsecondary education, employment, independent living 
and adult relationships.
• Older adults with disorders of intellectual development may present with a more rapid 
onset of dementia or declining skills than older adults in the general population. They 
also have significantly more difficulty gaining access to necessary support and appropriate 
health care for medical problems.
Neurodevelopmental disorders | Disorders of intellectual development

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Culture-related features
• The cultural appropriateness of tests and norms used to assess intellectual and adaptive 
functioning should be considered for each individual. Test performance may be affected 
by cultural biases (e.g. reference in test items to terminology or objects not common to a 
culture) and limitations of translation.
• In evaluating adaptive functioning (i.e. the individual’s conceptual, social and practical 
skills), the expectations of the individual’s culture and social environment should be 
considered.
• Language proficiency must also be considered when interpreting test results, in terms 
of both its impact on verbal performance and whether the individual understood 
the instructions.
Sex- and/or gender-related features
• The overall prevalence of disorders of intellectual development is slightly higher in 
males. The prevalence of some etiologies of disorders of intellectual development differs 
between males and females (e.g. X-linked genetic conditions such as fragile X syndrome 
are predominantly diagnosed in males, whereas Turner syndrome occurs exclusively in 
females).
• A number of associated features of disorders of intellectual development differ between 
males and females – for example, in the expression of problem behaviours and co-occurring 
mental, behavioural and neurodevelopmental disorders. Males are more likely to exhibit 
hyperactivity and conduct disturbances, whereas females are more likely to exhibit mood 
and anxiety symptoms.
• Reduced social value and expectations placed on females compared to males in some 
societies may negatively affect the accurate identification and provision of support for 
females with disorders of intellectual development.
Boundaries with other disorders and conditions (differential diagnosis)
Boundary with developmental speech and language disorders 
In developmental speech and language disorders, individuals exhibit difficulties in understanding or 
producing speech and language, or in using language in context for the purposes of communication 
that is markedly below what would be expected given the individual’s age and level of intellectual 
functioning. If speech and language abilities are significantly below what would be expected based 
on intellectual and adaptive behaviour functioning in an individual with a disorder of intellectual 
development, an additional diagnosis of developmental speech and language disorder may 
be assigned.
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Boundary with autism spectrum disorder
Autism spectrum disorder is characterized by persistent deficits in reciprocal social interaction and 
social communication, and by a range of restricted, repetitive, inflexible patterns of behaviour and 
interests. Although many individuals with autism spectrum disorder present with the significant 
limitations in intellectual functioning and adaptive behaviour observed in disorders of intellectual 
development, autism spectrum disorder can also present without general limitations in intellectual 
functioning. In cases of autism spectrum disorder where there are significant limitations in 
intellectual functioning and adaptive behaviour (i.e. 2 or more standard deviations below the mean 
or approximately less than the 2.3rd percentile) both the diagnosis of autism spectrum disorder 
using the with disorder of intellectual development specifier and the diagnosis of a disorder of 
intellectual development at the corresponding level of severity should be assigned. The diagnosis 
of autism spectrum disorder in individuals with severe and profound disorders of intellectual 
development is particularly difficult, and requires in-depth and longitudinal assessments. Because 
autism spectrum disorder inherently involves social deficits, assessment of adaptive behaviour as 
a part of the diagnosis of a co-occurring disorder of intellectual development should place greater 
emphasis on the conceptual and practical domains of adaptive functioning than on social skills.
Boundary with developmental learning disorders
Developmental learning disorders are characterized by significant and persistent difficulties in 
learning academic skills including reading, writing and arithmetic, with performance in these areas 
markedly below what would be expected based on chronological age or intellectual level. Individuals 
with disorders of intellectual development often present with limitations in academic achievement 
by virtue of significant generalized deficits in intellectual functioning. It is therefore difficult to 
establish the co-occurring presence of a developmental learning disorder in individuals with a 
disorder of intellectual development. However, developmental learning disorders can co-occur 
in some individuals with disorders of intellectual development if, despite adequate opportunities, 
acquisition of learning is significantly below what is expected based on established intellectual 
functioning. In such cases, both disorders may be diagnosed.
Boundary with developmental motor coordination disorders
In developmental motor coordination disorder, individuals exhibit significant delays during the 
developmental period in the acquisition of gross and fine motor skills, and impairment in the 
execution of coordinated motor skills that manifest in clumsiness, slowness or inaccuracy of motor 
performance. Individuals with disorders of intellectual development may also display such motor 
coordination difficulties that affect adaptive behaviour functioning. In contrast to those with 
developmental motor coordination disorder, individuals with disorders of intellectual development 
have accompanying significant limitations in intellectual functioning. However, if coordinated 
motor skills are significantly below what would be expected based on level of intellectual functioning 
and adaptive behaviour, and represent a separate focus of clinical attention, both diagnoses may 
be assigned.
Boundary with attention deficit hyperactivity disorder
In attention deficit hyperactivity disorder, individuals show a persistent and generalized pattern 
of inattention and/or hyperactivity-impulsivity that emerges during the developmental period. 
If all diagnostic requirements for a disorder of intellectual development are met, and inattention 
and/or hyperactivity-impulsivity are found to be outside normal expected limits based on age and 
level of intellectual functioning, with significant interference in academic, occupational or social 
functioning, both diagnoses may be assigned.
Boundary with dementia
In dementia, affected individuals – usually older adults – exhibit a decline from a previous level 
of functioning in multiple cognitive domains that interferes significantly with performance of 
Neurodevelopmental disorders | Disorders of intellectual development

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
activities of daily living. The disorders can co-occur, and some adults with disorders of intellectual 
development are at greater and earlier risk of developing dementia. For example, individuals 
with Down syndrome who exhibit a marked decline in adaptive behaviour functioning should be 
evaluated for the emergence of dementia. In cases in which the diagnostic requirements for both a 
disorder of intellectual development and dementia are met and describe non-redundant aspects of 
the clinical presentation, both diagnoses may be assigned.
Boundary with other mental and behavioural disorders
Other mental and behavioural disorders such as schizophrenia and other primary psychotic 
disorders may include symptoms that interfere with intellectual functioning and adaptive behaviour. 
A disorder of intellectual development should not be diagnosed if the limitations are better accounted 
for by another mental and behavioural disorder. However, other mental and behavioural disorders 
are at least as prevalent in individuals with disorders of intellectual development as in the general 
population, and co-occurring diagnoses should be assigned if warranted. In evaluating mental and 
behavioural disorders in individuals with disorders of intellectual development, signs and symptoms 
must be assessed using methods that are appropriate to the individual’s level of development and 
intellectual functioning, and may require a greater reliance on observable signs and the reports of 
others who are familiar with the individual.
Boundary with sensory impairments
If not addressed, sensory impairments (e.g. visual, auditory) can interfere with opportunities for 
learning, resulting in apparent limitations in intellectual functioning or adaptive behaviour. If the 
observed limitations are solely attributable to a sensory impairment, a disorder of intellectual 
development should not be assigned. However, prolonged sensory impairment throughout the 
critical period of development may result in the persistence of limitations in intellectual functioning 
or adaptive behaviour, despite later intervention, and an additional diagnosis of a disorder of 
intellectual development may be warranted in such cases.
Boundary with effects of psychosocial deprivation
Extreme psychosocial deprivation in early childhood can produce severe and selective impairments 
in specific mental functions such as language, social interaction and emotional expression. 
Depending on the onset, level of severity and duration of the deprivation, functioning in these 
areas may improve substantially after the child is moved to a more positive environment. However, 
some deficits may persist even after a sustained period in an environment that provides adequate 
stimulation for development, and a diagnosis of a disorder of intellectual development may be 
appropriate in such cases if all diagnostic requirements are met.
Boundary with neurodegenerative diseases
Neurodegenerative diseases can be associated with disorders of intellectual development but only 
if they have their onset in the developmental period (e.g. mucolipidosis type I, Gaucher’s disease 
type III). If a neurodegenerative disease co-occurs with a disorder of intellectual development, both 
diagnoses should be assigned.
Boundary with secondary neurodevelopmental syndrome
If the diagnostic requirements of a disorder of intellectual development are met and the symptoms 
are attributed to medical conditions with onset during the prenatal or developmental period, both 
disorder of intellectual development and the underlying medical conditions should be diagnosed. 
If the diagnostic requirements of a disorder of intellectual development are not met (e.g. limitations 
in intellectual functioning without limitations in adaptive functioning) and the symptoms are 
attributed to medical conditions with onset during the prenatal or developmental period, a diagnosis 
of secondary neurodevelopmental syndrome should be assigned, together with the diagnosis 
corresponding to the underlying medical condition.
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Table 6.1. Behavioural indicators of intellectual functioning
Severity level
Early childhood
Childhood and adolescence
Adulthood
Mild
By the end of this developmental 
period, there is evidence of 
the emergence or presence of 
the abilities listed below.
• Most will develop language skills 
and be able to communicate 
needs. Delays in the acquisition 
of language skills are typical, 
and once acquired the skills are 
frequently less developed than 
in typically developing peers 
(e.g. more limited vocabulary).
• Most can tell or identify 
their gender and age.
• Most can attend to a simple 
cause-effect relationship.
• Most can attend to and follow 
up to 2-step instructions.
• Most can make one-to-one 
correspondence or match 
to sample (e.g. organize 
or match items according 
to shape, size, colour).
• Most can communicate their 
immediate future goals (e.g. 
desired activities for the day).
• Most can express their likes and 
dislikes in relationships (e.g. who 
they prefer to spend time with), 
activities, food and dress.
Literacy/numeracy
• Most will develop emergent 
reading and writing skills.
• Most will be able to recognize 
letters from their name, 
and some can recognize 
their own name in print.
During this developmental 
period, there is evidence of 
the emergence or presence of 
the abilities listed below.
• Most can communicate effectively.
• Most can tell or identify their age.
• Most can initiate/invite others 
to participate in an activity.
• Most can communicate about 
past, present and future events.
• Most can attend to and follow 
up to 3-step instructions.
• Most can identify different 
denominations of money 
(e.g. coins) and count small 
amounts of money.
• Most can cross street intersections 
safely (look in both directions, 
wait for traffic to clear before 
crossing, obey traffic signals). 
In contexts without busy 
intersections, most can follow 
socially acceptable rules necessary 
to ensure personal safety.
• Most can communicate their 
future goals and participate 
in their health care.
• Most can identify many of their 
relatives and their relationships.
• Most can apply existing abilities 
in order to build skills for future 
semi-skilled employment (i.e. 
involving the performance of 
routine operations) and in some 
cases skilled employment (e.g. 
requiring some independent 
judgement and responsibility).
• Most are naive in anticipating 
full consequences of actions 
or recognizing when someone 
is trying to exploit them.
• Some can orient themselves 
in the community and travel 
to new places using familiar 
modes of transportation.
Literacy/numeracy
• Most can read sentences 
with five common words.
• Most can count and make simple 
additions and subtractions.
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• Most can communicate fluently.
• Many can tell or identify 
their birth date.
• Most can initiate/invite others 
to participate in an activity.
• Most can communicate about 
past, present and future events.
• Most can attend to and follow 
up to 3-step instructions.
• Most can identify different 
denominations of money 
(e.g. coins) and count money 
more or less accurately.
• Most can orient themselves 
in the community and learn 
to travel to new places using 
different modes of transportation 
with instruction/training.
• Some can learn the road laws 
and meet requirements to obtain 
a driver’s license. Travel is mainly 
restricted to familiar environments.
• Most can cross residential street 
intersections safely (look in both 
directions, wait for traffic to clear 
before crossing, obey traffic 
signals). In contexts without busy 
intersections, most can follow 
socially acceptable rules necessary 
to ensure personal safety.
• Most can communicate their 
decisions about their future goals, 
health care and relationships (e.g. 
who they prefer to spend time with).
• Most can apply existing abilities in the 
context of semi-skilled employment 
(i.e. involving the performance 
of routine operations) and in 
some cases skilled employment 
(e.g. requiring some independent 
judgement and responsibility).
• Most remain naive in anticipating 
full consequences of actions 
or recognizing when someone 
is trying to exploit them.
• Most have difficulty in handling 
complex situations such as 
managing bank accounts and 
long-term money management.
Literacy/numeracy
• Most can read and write up to 
approximately a level expected 
for someone who has attended 
7–8 years of schooling (i.e. start 
of middle/secondary school), 
and read simple material for 
information and entertainment.
• Most can count, understand 
mathematical concepts and make 
simple mathematical calculations.

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Table 6.1. contd
Severity level
Early childhood
Childhood and adolescence
Adulthood
Moderate
• Most will develop language skills 
and be able to communicate 
needs. Delays in the acquisition 
of language skills are typical, 
and once acquired the skills 
are often less developed than 
in typically developing peers 
(e.g. more limited vocabulary).
• Most can follow 1-step instructions.
• Most can self-initiate activities and 
participate in parallel play. Some 
develop simple interactive play.
• Some can attend to a simple 
cause-effect relationship.
• Most can distinguish between 
“more” and “less”.
• Some can make one-to-one 
correspondence or match 
to sample (e.g. organize 
or match items according 
to shape, size, colour).
• Many can express their likes and 
dislikes in relationships (e.g. who 
they prefer to spend time with), 
activities, food and dress.
Literacy/numeracy
• Most can recognize symbols.
• Most can tell or identify 
their age and gender.
• Most can initiate/invite others 
to participate in an activity.
• Most can communicate 
immediate experiences.
• Most can attend to and follow 
up to 2-step instructions.
• Some can cross residential street 
intersections safely (look in both 
directions, wait for traffic to clear 
before crossing, obey lights and 
signal signals). In contexts without 
busy intersections, some can follow 
socially acceptable rules necessary 
to ensure personal safety.
• Some can go independently 
to nearby familiar places.
• Most can communicate 
preferences about their future 
goals when provided with options.
• Most can express their likes and 
dislikes in relationships (e.g. who 
they prefer to spend time with), 
activities, food and dress.
• With support, most can apply 
existing abilities in order to build 
skills for future semi-skilled 
employment (i.e. involving the 
performance of routine operations).
• Most are naive in anticipating 
full consequences of actions 
or recognizing when someone 
is trying to exploit them.
Literacy/numeracy
• Most will develop emergent 
reading and writing skills.
• Most can recognize their 
own name in print.
• Most can choose the correct 
number of objects.
• Some can learn to count up to 10.
• Most can initiate/invite others 
to participate in an activity.
• Most can communicate 
immediate experiences.
• Most can attend to and follow 
up to 2-step instructions.
• Most can cross residential street 
intersections safely (look in both 
directions, wait for traffic to clear 
before crossing, obey lights and 
signal signals). In contexts without 
busy intersections, some can follow 
socially acceptable rules necessary 
to ensure personal safety.
• Some can travel independently 
to familiar places.
• Most can communicate their 
preferences about their 
future goals, health care and 
relationships (e.g. who they 
prefer to spend time with), and 
will often act in accordance 
with these preferences.
• Some can apply existing abilities 
in the context of semi-skilled 
employment (i.e. involving the 
performance of routine operations).
• Most remain naive in anticipating 
full consequences of actions 
or recognizing when someone 
is trying to exploit them.
Literacy/numeracy
• Most can read sentences with 
three common words and can 
achieve a reading and writing level 
up to that expected of someone 
who has attended 4–5 years of 
schooling (i.e. several years of 
primary/elementary school).
• Most can choose the correct 
number of objects.
• Most can count to 10 and 
in some cases higher.
Severe
• Most will develop various 
simple nonverbal strategies 
to communicate basic needs.
• Some can self-initiate activities.
• Most can attend to and 
respond to others.
• Most can separate one object 
from a group upon request.
• Most can stop an activity 
upon request.
• Most can use communication 
strategies to indicate preferences.
• Most can self-initiate activities.
• Most can attend to and 
recognize familiar pictures.
• Most can follow 1-step instructions 
and stop an activity upon request.
• Most can distinguish between 
“more” and “less”.
• Most can separate one object 
from a group upon request.
• Most can use communication 
strategies to indicate preferences.
• Most can self-initiate activities.
• Most can attend to and 
recognize familiar pictures.
• Most can follow 1-step instructions 
and stop an activity upon request.
• Most can distinguish between 
“more” and “less”.
• Most can separate one object 
from a group upon request.
Neurodevelopmental disorders | Disorders of intellectual development

103
Severity level
Early childhood
Childhood and adolescence
Adulthood
• Most can express their likes and 
dislikes in relationships (e.g. who 
they prefer to spend time with), 
activities, food and dress when 
given concrete choices (e.g. with 
visual aids).
Literacy/numeracy
• Most can make rudimentary marks 
that are precursors to letters on 
a page.
• Most can differentiate locations 
and associate meanings (e.g. car, 
kitchen, bathroom, school, doctor’s 
office).
• Most can express their likes and 
dislikes in relationships (e.g. who 
they prefer to spend time with), 
activities, food and dress when 
given concrete choices (e.g. with 
visual aids).
• With support, some may be able 
to apply existing abilities in order 
to build skills for future unskilled 
employment (i.e. involving 
performing simple duties) or semiskilled employment (i.e. involving 
performing routine operations).
Literacy/numeracy
• Most can recognize symbols.
• Many can recognize own name 
in print.
• Most can differentiate locations 
and associated meanings (e.g. car, 
kitchen, bathroom, school, doctor’s 
office).
• Most can communicate their 
preferences about their future 
goals, health care and relationships 
(e.g. who they prefer to spend time 
with) when given concrete choices 
(e.g. with visual aids).
• Some can apply existing skills 
to obtain unskilled employment 
(i.e. involving performing simple 
duties) or semi-skilled employment 
(i.e. involving performing routine 
operations) with appropriate social 
and visual/verbal support.
Literacy/numeracy
• Most can recognize common 
pictures (e.g. house, ball, flower).
• Many can recognize letters from 
an alphabet.
Profound
• Many will develop nonverbal 
strategies to communicate 
basic needs.
• Most can attend to and respond 
to others.
• Most can start or stop activities 
with prompts and aids.
• Many can express their likes and 
dislikes in relationships (e.g. who 
they prefer to spend time with), 
activities, food and dress when 
given concrete choices (e.g. with 
visual aids).
Literacy/numeracy
• Children with profound disorders 
of intellectual development will not 
learn to read or write.
• Most will develop strategies to 
communicate basic needs and 
preferences.
• Most can recognize familiar people 
in person and in photographs.
• Most can perform very simple tasks 
with prompts and aids.
• Some can separate one object from 
a group upon request.
• Some can differentiate locations 
and associated meanings (e.g. car, 
kitchen, bathroom, school, doctor’s 
office).
• Many can express their likes and 
dislikes in relationships (e.g. who 
they prefer to spend time with), 
activities, food and dress when 
given concrete choices (e.g. with 
visual aids).
• Most will develop nonverbal 
strategies and some utterances/
occasional words to communicate 
basic needs and preferences.
• Most can attend to and recognize 
familiar pictures.
• Most can perform very simple tasks 
with prompts and aids.
• Some can separate one object from 
a group upon request.
• Some can differentiate locations 
and associated meanings (e.g. 
car, kitchen, bathroom, school, 
doctor’s office).
• Many can communicate their 
preferences about their future 
goals, health care and relationships 
(e.g. who they prefer to spend time 
with) when given concrete choices 
(e.g. with visual aids).
Table 6.1. contd
Neurodevelopmental disorders
Neurodevelopmental disorders | Disorders of intellectual development
Note: the presence or absence of particular behavioural indicators listed in the table is not sufficient to assign a diagnosis of disorder of intellectual development. 
Clinical judgement is a necessary component in determining whether an individual has a diagnosable disorder, and diagnosis relies on the following key assumptions being met:
• Limitations in present functioning have been considered within the context of community environments typical of the individual’s age peers and culture.
• Valid assessment has considered cultural and linguistic diversity, as well as differences in communication, sensory, motor and behavioural factors.
• Within an individual, limitations are recognized to often coexist alongside strengths and both were considered during the assessment.
• Limitations are described, in part, to develop a profile of needed support.
• It is recognized that with appropriate support over a sustained period, the life functioning of the affected person generally will improve.
• Please consult the CDDR for disorders of intellectual development and, if applicable, autism spectrum disorder for guidance on how to determine the severity level.

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Table 6.2. Behavioural indicators of adaptive behaviour, early childhood (up to 6 years of age)
Severity level
Conceptual
Social
Practical
Mild
• Most can perform basic listening 
skills with a 15-minute attention 
span. They will need help to sustain 
their attention for 30 minutes.
• Most are able to follow simple 
2-step instructions. They will 
need help following a 3-step or 
“if-then” type of instruction.
• Most can state their age and 
name and identify close family 
members when asked.
• Many will have a 100-word 
vocabulary. Most will ask “wh” 
question (who, what, where, 
why), but will need help using 
pronouns and tense verbs.
• Most are not able to give a detailed 
account of their experiences.
• Most will understand the simple 
concepts of time, space, distance 
and spatial relationships.
Literacy
• Many will not learn reading/
writing skills. If present, reading 
skills will be limited to identifying 
some letters of the alphabet. Only 
some will be able to recognize 
their own name in print.
• Most can perform independently 
basic skills related to social 
interaction – such as imitation 
and showing affection to familiar 
people, as well as friend-seeking 
behaviour – expressing emotions 
and answering basic questions.
• Most will need frequent 
encouragement and assistance 
in offering help to others, sharing 
interests or perspective taking. 
They are able to engage in play 
with others, even with minimal 
supervision, although they will 
need assistance taking turns, 
following rules or sharing.
• Most are able to demonstrate 
polite behaviour (saying “please”, 
“thank you”), although they 
may need help apologizing, 
demonstrating appropriate 
behaviour with strangers or waiting 
for the appropriate moment to 
speak in a social context.
• Most will need help to modify their 
behaviour in accordance with 
changing social situations or when 
there is a change in their routines.
• Most will learn the majority of basic 
eating, washing face and hands, 
toileting and self-care skills.
• Most will acquire independence 
in dressing (nut may need 
help to button/fasten clothes) 
and night-time continence.
• Most can use simple 
household devices.
• Most will need support with 
bathing, using utensils, toileting 
such as cleaning after passing 
stools, and brushing teeth.
• Most can learn the concept of 
danger and avoid hot objects.
• Most will be able to help with 
simple household chores 
independently, but will often need 
assistance with more complex 
tasks such as putting away clothes 
or cleaning up their rooms.
• With some assistance, most 
can learn the concept of money 
(although they will be unable to 
learn the value of the different 
denominations, e.g. coins), 
can count to 10, and can follow 
basic rules around the home.
• Most will be unable to learn 
days of the week, and learn and 
remember phone numbers.
Moderate
• Most will independently point to 
common objects when asked and 
follow 1-step instructions. Some 
will need support to perform 
basic skills such as following 
simple 2-step instructions.
• Most can state their own name.
• Most will have basic 
communication skills such as 
formulating one-word requests, 
using simple phrases and using 
other people’s customary forms 
of address (mommy, papa, sister), 
but will need help with full names.
• Most will speak at least 50 
words and name/point to at 
least 10 objects when asked.
• Most are not able (or will 
need considerable support) 
to use past tense verbs, 
pronouns or “wh” questions.
Literacy
• Most will not learn reading or 
writing skills, but will know 
how to use pens and pencils 
and make marks on a page.
• Most are able to perform 
independently some of the basic 
skills related to social interaction, 
although they might need 
some help making new friends, 
answering basic social questions 
or expressing their emotions.
• Most are able to play with peers 
and show interest in, play or 
interact with others, but may need 
more supervision/support to play 
cooperatively with others, play 
symbolically, take turns, follow 
rules of a game and share objects.
• Most will not be able to perform 
more complex social skills involving 
interpersonal interactions such as 
offering help to others, empathy, 
sharing their interests with 
others or perspective taking.
• Most can learn the majority of 
basic eating skills, but may need 
more assistance than their sameage peers with toilet training 
and dressing themselves (some 
help needed to button/fasten).
• Most will learn to ask to use the 
toilet, drink from a cup, feed 
themselves with a spoon, and 
some may become toilet trained 
during daytime. Most will often 
need support with brushing teeth, 
bathing and using utensils.
• With some support, most can learn 
to use simple household devices 
and carry out simple chores such 
as putting away their footwear.
• Most can learn the concept of 
danger, although some assistance 
will be needed when using 
sharp objects (e.g. scissors).
• Many will be able to help with very 
simple household chores such as 
cleaning fruits and vegetables.
• Most will not acquire understanding 
of the concept of money and time.
Neurodevelopmental disorders | Disorders of intellectual development

105
Severity level
Conceptual
Social
Practical
Severe
• Most can perform independently 
the most basic skills such as wave 
goodbye, identify parent/caregiver, 
point to a desired object and 
point or gesture to indicate their 
preference, and understanding 
the meaning of yes and no.
• Most will need support to point 
to/identify common objects, 
follow 1-step instructions, and 
sustain their attention to listen to 
a story for at least 5 minutes.
• Most will not be able to state 
their age correctly and will speak 
less than 50 recognizable words. 
They may need help formulating 
1-word requests and using 
first names or nicknames of 
familiar people, naming objects, 
answering when called upon, 
and using simple phrases.
Literacy
• Most will not learn reading 
and writing skills.
• Most will need help to perform 
basic social skills such as 
imitation or showing interest 
and preferences in social 
interactions with their peers.
• Most are able to show interest 
when someone else is playful 
and to play simple games.
• Most will need significant support 
to play in a cooperative way, 
play symbolically or seek others 
for play/leisure activities.
• Most will need significant help 
with transitions – changing from 
one activity to another or an 
unexpected change in routine.
• Most will need significant help 
using polite social responses such 
as “please” and “thank you”.
• Most will not be able to engage 
in turn-taking, following 
rules or sharing objects.
• Most can learn many of the 
basic eating skills but will need 
substantially more assistance than 
their same-age peers with toilet 
training, learning to use a cup and 
spoon, and putting on clothes.
• Most can learn to use simple 
household devices with 
consistent support.
• Most will have difficulty 
learning to master many selfcare skills, including using 
the toilet independently.
• Most will not be able to learn 
the concept of danger, and 
will require close supervision 
in areas such as the kitchen.
• Some may learn basic cleaning 
skills such as washing hands but 
will consistently need assistance.
• Most will not learn the concept 
of money, time or numbers.
Profound
• Most will master only the most 
basic communication skills 
such as turning their eye gaze 
and head towards a sound.
• Children with profound disorders 
of intellectual development will 
typically need prompting to 
orient towards people in their 
environment, respond when their 
name is called, and understand 
the meaning of yes and no.
• Children with profound disorders 
of intellectual development 
are typically able to cry when 
hungry or wet, smile and make 
sounds of pleasure, but it may be 
difficult to get their attention.
Literacy
• Children with profound disorders 
of intellectual development will 
not learn to read or write.
• Most may be able to perform 
only the most basic social skills 
such as smiling, orienting their 
gaze, looking at others/objects, 
or showing basic emotions.
• Some might be able to perform 
other basic social skills 
with considerable support/
prompting, such as showing 
preference for people or objects, 
imitating simple movements 
and expressions, or engaging in 
reciprocal social interactions.
• Some can show interest when 
someone else is playful, but 
will need considerable support 
to play simple games.
• Most will have difficulty 
adapting to changes and 
transitions in activity/location.
• Most will be unable to follow 
rules of a social game.
• Most will need help 
performing even the most 
basic eating, dressing, 
drinking and bathing skills.
• Most will be unable to learn 
to be independent using the 
toilet, being dry during the day, 
bathing or washing self at the 
sink, and using a fork and knife.
• Most will need constant 
supervision around potentially 
dangerous situations in the 
home and community.
• Most will be unable to clean up 
after themselves and will need help 
with even basic chores, such as 
picking up belongings to put away.
• Most will not be able to learn 
to use the telephone or other 
simple devices around the 
home independently.
Note: the behavioural indicators in the table are intended to be used by the clinician in determining the level of severity of the disorder of intellectual development, either as a 
complement to properly normed, standardized tests, or when such tests are unavailable or inappropriate given the individual’s cultural and linguistic background. Use of these 
indicators is predicated on the clinician’s knowledge of and experience with typically developing individuals of comparable age. Unless explicitly stated, the behavioural indicators 
of intellectual functioning and adaptive behaviour functioning for each severity level are what are typically expected to be mastered by the individual by 6 years of age. Please 
consult the CDDR for disorders of intellectual development and, if applicable, autism spectrum disorder for guidance on how to determine the severity level.
Table 6.2. contd
Neurodevelopmental disorders
Neurodevelopmental disorders | Disorders of intellectual development

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Table 6.3. Behavioural indicators of adaptive behaviour, childhood and adoles­
cence (6–18 years of age)
Severity level
Conceptual
Social
Practical
Mild
• Most will need some help 
to sustain their attention 
for a 30-minute period.
• Most can follow 3-step instructions.
• Most will acquire sufficient 
communication skills to use 
pronouns, possessives and 
regular tenses, as well as be able 
to ask “wh” question (e.g. who, 
what, where, when or why).
• Many will need support to tell a 
narrative story or to give someone 
simple directions. They will also 
need assistance to explain their 
ideas using multiple examples, 
detail short-term goals and steps 
to achieve them, stay on the 
topic in group conversations and 
move from one topic to another.
Literacy
• Most will have reading and 
writing skills that are limited to 
approximately those expected of 
someone who has attended 3–4 
years of primary/elementary school. 
• Some may have a more concrete 
understanding of social 
situations, and may need support 
understanding some types of 
humour (e.g. teasing others), 
making plans and knowing to let 
others know about these plans as 
needed, controlling their emotions 
when faced with disappointment, 
and knowing to avoid dangerous 
activities or situations that may 
not be in their best interest (e.g. 
taken advantage of or exploited).
• Some may need some support 
initiating conversation, 
organizing social activities with 
others or talking about shared 
interests with peers/friends.
• Some may need substantial 
support to talk about personal 
things and emotions or 
understand social cues.
• Most are able to play outdoor 
sports or other social games in 
groups, although they need help 
to play games with more complex 
rules (e.g. board games).
• Most will learn to perform 
independently most dressing, 
toileting and eating skills.
• Most will learn to manage 
activities of daily living 
independently, such as brushing 
teeth, bathing and showering.
• Most will need some support 
getting around the community and 
being safe (e.g. although they will 
know to stay to the side of routes 
with car traffic, they may continue 
to need support to check for 
traffic before crossing a street).
• Many may be vulnerable to being 
taken advantage of in social 
situations. They may continue to 
need some support for telling time, 
identifying correct day/dates on 
calendar, making and checking 
the correct change at the store, 
and being independent with basic 
health-maintaining behaviours.
• If available, many can learn 
to use computers and cell 
phones for school and play.
• Most will learn basic work 
skills at nearly the same pace 
as their same-age peers, but 
will require greater repetition 
and structure for mastery.
Moderate
• Most will need help performing 
skills such as following instructions 
containing “if-then”, and sustaining 
their attention to listen to a story 
for at least a 15-minute period.
• Most can say at least 100 
words, use negatives, use 
simple sentences and state their 
first and last name and their 
locality/place of residence.
• Some may need help using 
pronouns, possessives 
or past tense verbs.
• Some may need support 
telling basic parts of a story 
or asking “wh” questions (e.g. 
when, where, why, who).
• Most will not learn complex 
conversation skills (i.e. expressing 
their ideas in an abstract manner 
or in more than one way).
• Some may need support 
expressing their emotions or 
concerns, knowing when others 
might need their help, showing 
emotions appropriate to the 
situation/context, or knowing 
what others like or want.
• Most will need considerable help 
initiating a conversation, waiting 
for the appropriate moment to 
speak, meeting friends and going 
on social outings or talking about 
shared interests with others.
• Most will need help following 
rules when playing simple games 
or going out with friends.
• Some will need support when 
changing routines and transitioning 
between activities/places.
• Most can learn to feed 
themselves, use the toilet and 
dress (including putting shoes/
footwear on the correct feet).
• Most will often continue to need 
support to attain independence 
for bathing and showering, 
brushing teeth, selecting 
appropriate clothing, and 
being independent and safe in 
the home and community.
• Most will continue to have difficulty 
using a knife to cut food, using 
cooking appliances safely, using 
household products safely, and 
doing household chores.
Neurodevelopmental disorders | Disorders of intellectual development

107
Severity level
Conceptual
Social
Practical
Literacy
• Most will have reading and 
writing skills that will be limited to 
approximately those expected of 
someone who has attended 2 years 
of primary/elementary school.
• Most may need support with 
reading simple stories, writing 
simple sentences, and writing more 
than 20 words from memory.
• Most will be able to say the 
names of a few animals, fruits 
and foods prepared in the home.
• Some will need support in behaving 
appropriately in accordance 
with social situations, and 
knowing what to do in social 
situations involving strangers.
• Most individuals will not be 
able to share information with 
others about their past day’s 
events/activities, and will need 
support managing conflicts or 
challenging social interactions 
and recognizing/avoiding 
dangerous social situations.
• Most will not acquire an 
understanding of taking 
care of their health.
• Most will learn basic work skills 
but later than same-age peers
Severe
• Most will be able independently 
to make simple one-word 
requests, use first names of 
familiar individuals and name 
at least 10 familiar objects.
• Some may need help following 
instructions, and will not 
be able to use pronouns, 
possessives or regular past 
tenses, or state their age.
• With help, some may be able 
to ask “wh” questions (e.g. 
when, why, what, where), use at 
least 100 recognizable words, 
use negatives, and relate their 
experiences in simple sentences.
Literacy
• Most will have reading and 
writing skills that will be 
limited to identifying some 
letters of the alphabet.
• Most will be able to count up to 5.
• Some may need support 
demonstrating friend-seeking 
behaviour, or engaging in 
reciprocal social interactions.
• Most will need help expressing 
their emotions or showing empathy.
• Most will not know that they should 
offer help to others without cues 
or prompting, show appropriate 
emotions in social situations, 
engage in conversations or ask 
others about their interests.
• Most will need support to 
play cooperatively.
• Most will need help with 
transitions – changing from 
one activity to another, or an 
unexpected change in routine.
• With considerable help, some might 
be able to start/end a conversation 
appropriately, and say “please” and 
“thank you” when appropriate.
• Most will have difficulty 
following social rules, as well 
as rules associated with games 
such as turn-taking or sharing 
toys. Most will be unable to 
participate in social or other 
games with complex rules.
• Most can learn to independently 
put on and take off clothing, 
feed themselves with hand or 
a spoon, and use the toilet.
• They will often continue to need 
support to attain independence 
for putting shoes or other 
footwear on the correct feet, 
buttoning and fastening clothing, 
bathing and showering.
• Most individuals will not learn 
the rules and safe behaviours 
in the home and community, 
doing household chores or 
checking for correct change 
when purchasing items.
• Some will learn basic work skills 
but later than same-age peers.
Table 6.3. contd
Neurodevelopmental disorders
Neurodevelopmental disorders | Disorders of intellectual development

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Severity level
Conceptual
Social
Practical
Profound
• Most will have basic 
communication skills such as 
orienting their eye gaze and turning 
their head to locate a sound, 
responding to their name, getting 
a parent/caregiver’s attention, 
expressing their needs, and 
demonstrating an understanding 
of the meaning of yes and no.
• With significant support, some 
will be able to wave goodbye, 
use their parent/caregiver’s 
name, and point to objects to 
express their preferences.
• Most indicate when there are 
hungry or wet by making a 
vocalization or crying, smile, 
and make sounds to indicate 
they are happy/sad.
• Some may not be able to 
effectively use communication 
to get the attention of others 
in their environment.
Literacy
• Most will not learn to read or write.
• Most will need some help to 
perform basic social skills 
such as showing interest and 
affection for people familiar 
to them, engaging in social 
interactions, or discriminating 
between acquaintances.
• Some can perform certain social 
skills such as imitation, showing 
interest in peers or empathy.
• For some, transitioning between 
social contexts and activities 
will elicit negative reactions 
if not done with support.
• Most will not be able to engage in 
cooperative social play, and will 
need a lot of help moderating their 
behaviour to different social cues. 
• Most will need exceptional 
support with basic hygiene 
and washing, picking up after 
themselves, clearing their place 
at the kitchen table, being safe in 
the kitchen, and using hot water.
• Most will be unable to learn 
to prepare foods or assist in 
the kitchen, or use simple 
household devices (e.g. 
switches, stoves, microwaves).
• Most will not learn rules 
and safe behaviours in the 
home and community.
• Most will require a lot of 
supervision to remain on task and 
be engaged in basic vocational 
or pre-vocational skills.
Table 6.3. contd
Note: the behavioural indicators in the table are intended to be used by the clinician in determining the level of severity of the disorder of intellectual development, either as a 
complement to properly normed, standardized tests, or when such tests are unavailable or inappropriate given the individual’s cultural and linguistic background. Use of these 
indicators is predicated on the clinician’s knowledge of and experience with typically developing individuals of comparable age. Unless explicitly stated, the behavioural indicators 
of intellectual functioning and adaptive behaviour functioning for each severity level are what are typically expected to be mastered by the individual by 18 years of age. Please 
consult the CDDR for disorders of intellectual development and, if applicable, autism spectrum disorder for guidance on how to determine the severity level.
Neurodevelopmental disorders | Disorders of intellectual development

109
Table 6.4. Behavioural indicators of adaptive behaviour, adulthood (18 years of age and over)
Severity level
Early childhood
Childhood and adolescence
Adulthood
Mild
• Most will master listening and 
communication skills, although 
some may need help to stay on 
topic in group conversations, move 
from one topic to another, express 
ideas in more than one way or state 
their complete home address.
• Most will probably not be able 
to give complex directions and 
describe long-term goals.
Literacy
• Most can read and understand 
material up to that expected of 
someone who has attended 3 or 
4 years of primary/elementary 
school, and will master some 
writing skills, although they 
may have difficulty writing 
reports and long essays.
• Most can meet others 
independently for the purpose of 
making new friends, participate in 
social outings on a regular basis, 
and talk about personal feelings.
• Most can initiate a conversation 
independently and talk about 
shared interests with others.
• Most can understand social 
cues, and are able to regulate 
their conversation based 
on their interpretation of 
other people’s feelings.
• Most are able to play complex 
social games and team sports, 
although they may need support 
with understanding the rules.
• Most can learn to weigh the 
possible consequences of their 
actions before making a decision 
in familiar situations but not in 
new or complex situations, and 
will know right from wrong.
• Most will need help recognizing 
when a situation or relationship 
might pose dangers or 
someone might be manipulating 
them for their own gain.
• Most can initiate planning of a 
social activity with others. Some 
can be engaged in an intimate 
relationship, whereas others might 
need more support to do so.
• Most will be independent in 
household chores, be safe 
around the home, and use the 
telephone and TV; some will learn 
to operate a gas or electric stove.
• Most will often continue to 
need some support to attain 
independence with more complex 
domestic skills (e.g. small 
household repairs), comparative 
shopping for consumer products, 
following a healthy diet and being 
engaged in health-promoting 
behaviours, caring for themselves 
when sick or knowing what to 
do when they are sick/ill.
• Many can learn to live and work 
independently, working at a 
part-time or full-time job with 
competitive wages – support at 
work will depend on the level of 
complexity of the work, and may 
fluctuate with life transitions.
• Some can learn to drive a motor 
vehicle or a bicycle, manage simple 
aspects of a bank account, prepare 
simple meals and, if available, 
use a computer or other digital 
devices. Many will learn to use 
public transport with minimal help.
• Most will continue to need support 
with more complex banking 
needs, paying bills, driving on 
busy roads and parenting skills.
Moderate
• Most will need considerable 
support to be able to attend 
to various tasks for more 
than a 15-minute period 
and to follow instructions 
or directions from memory 
(i.e. with a 5-minute delay).
• Most will master simple 
descriptions, using “wh” questions 
(e.g. what, when, why, where) 
and relating their experiences 
using simple sentences.
• With help, most are able to 
follow 3-step instructions.
• Most will continue to need 
help frequently with using 
language containing past 
tenses and describing their 
experiences in detail.
• Most will not learn more complex 
conversation skills (e.g. expressing 
ideas in more than one way).
• Some will need help learning 
how to share interests or 
engaging in perspective taking.
• Some may need support initiating 
conversations and introducing 
themselves to unfamiliar people.
• Most will need significant 
support engaging in regular 
social activities, planning 
social activities with others, 
understanding social cues, and 
knowing what are appropriate or 
inappropriate conversation topics.
• Most will need significant support 
engaging in social activities 
requiring transportation.
• Most are unable to be engaged in 
more social or other games with 
complex rules (e.g. board games).
• Some will learn to master dressing 
(but may need some help 
selecting appropriate clothing 
to wear for weather), washing, 
eating and toileting needs.
• Most are able to be safe around 
the home, use the telephone, 
use the basic features of a TV 
and use simple appliances/
household articles (e.g. switches, 
stoves, microwaves).
• Some may continue to need 
support with bathing and 
showering, using more complex 
household appliances (e.g. stoves) 
safely, meal preparation, or 
using cleaning products safely.
• Many will understand the function 
of money but will struggle with 
making change, budgeting 
and making purchases without 
being told what to buy.
Neurodevelopmental disorders
Neurodevelopmental disorders | Disorders of intellectual development

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Severity level
Early childhood
Childhood and adolescence
Adulthood
Literacy
• Most will acquire some reading 
and writing skills, such as letters of 
the alphabet, writing at least three 
simple words from an example, 
and writing their own first and last 
name. They will need significant 
support to write simple sentences 
or read simple stories at about 
the level expected of someone 
who has attended 2 years of 
primary/elementary school.
• Most will need help providing 
socially polite responses such 
as “please” and “thank you”.
• Most are unable to recognize 
when a social situation might 
pose some danger to them (e.g. 
potential for abuse or exploitation).
• Most will need support being 
safe in the community and 
living independently. They 
will need substantial support 
for employment, including 
finding and keeping a job.
• Most will not be able to travel 
independently to new places, 
have a developed concept of time 
sufficient to tell time independently 
and know when they are late.
Severe
• Most will often need lifelong 
support to recall and comply 
with instructions given 5 minutes 
prior, and sustain their attention 
to a story for a 15-minute 
period. Most are able to listen 
and attend to a story for a 
period of at least 5 minutes.
• Most can make sounds or gestures 
to get the attention of individuals 
in their environment, and can 
make their needs known.
• They may need help using simple 
phrases, describing objects and 
relating their experiences to others, 
speaking at least 100 recognizable 
words, and using negatives, 
possessives and pronouns, 
and asking “wh” questions.
Literacy
• Reading and writing skills will be 
limited to identifying some letters 
of the alphabet, copying simple 
words from an example and 
attempting to write their name.
• All will need help in social 
situations, showing and expressing 
their emotions in an appropriate 
manner, and engaging in a 
reciprocal conversation with others.
• Most can play simple social games 
such as catching and throwing a 
ball, but may need help choosing 
friends to play with. They will 
need considerable help to play 
symbolically and follow the rules 
while playing games, such as 
turn-taking or sharing toys.
• Most will need help with 
transition – changing from 
one activity to the next or an 
unexpected change in routine.
• Most will not spontaneously use 
polite forms such as “please”, 
“excuse me”, “thank you” and 
so on, or respectful/customary 
ways of addressing others. They 
will need significant support 
starting, maintaining and ending 
conversations with others.
• Most will not recognize when 
a social situation might pose a 
danger to them (e.g. potential 
for abuse or exploitation) or 
discern dangers potentially 
associated with strangers.
• Most will need some support 
for even basic personal 
hygiene, domestic skills, home 
and community skills.
• Most will be able to drink 
independently from a cup and 
learn to use basic utensils for 
eating. Some may continue to 
need support getting dressed.
• Many may learn independent 
toileting if provided an established 
routine. Most will be unable to care 
for their own belongings, perform 
household chores independently, 
cooking or care for their health.
• Most will need substantial 
support to travel independently, 
plan and do shopping and 
banking of any sort.
• Most will require significant support 
to be engaged in paid employment.
Profound
• Most are able to turn their head 
and eye gaze towards sounds in 
their environment and respond 
to their name when called.
• Most will use sounds and gestures 
to get a parent/caregiver’s 
attention or express their 
wants, and some will have an 
understanding of the meaning of 
yes and no. Some are able with 
prompting to wave goodbye, use 
their parent’s/caregiver’s name /
customary ways of addressing 
others, and point to objects to 
express their preferences.
• Most will not spontaneously 
show interest in peers or 
unfamiliar individuals.
• With significant support, 
most are able to imitate 
simple actions/behaviours or 
show concern for others.
• Most will not engage in reciprocal/
back-and-forth conversation.
• Most will not spontaneously use 
polite forms such as “please”, 
“excuse me”, “thank you” and so on.
• Most will need support performing 
even the most basic self-care, 
eating, washing and domestic skills.
• Some may learn independent 
toileting during the day, 
but night-time continence 
will be more difficult.
• Most will have difficulty picking 
out appropriate clothing, and 
zipping and snapping clothes.
• Most will need supervision and 
support for bathing, including 
safely adjusting water temperature 
and washing/drying.
Table 6.4. contd
Neurodevelopmental disorders | Disorders of intellectual development

111
Table 6.4. contd
Severity level
Early childhood
Childhood and adolescence
Adulthood
Profound
• Most will cry or make vocalizations 
when hungry or wet, smile, and 
make sounds of pleasure.
• Most are not able to follow 
instructions or story being told.
• Most will have only rudimentary 
knowledge of moving around 
within their house.
Literacy
• Most will not learn to read or write.
• Most are unable to anticipate 
changes in routines. Social 
interactions with others will 
be very basic and limited to 
essential wants and needs.
• Most are unable to recognize 
when a social situation might 
pose some danger to them (e.g. 
potential for abuse or exploitation).
• Most will be unable to clean or 
care for their living environment 
independently, including clothing 
and meal preparation.
• All will need substantial support 
with health matters, being safe 
in the home and community, and 
learning the concept of days 
of the week and time of day.
• Most will be extremely limited 
in their vocational skills, and 
engagement in employment 
activities will necessitate 
structure and support.
Note: the behavioural indicators in the table are intended to be used by the clinician in determining the level of severity of the disorder of intellectual development either as 
a complement to properly normed, standardized tests, or when such tests are unavailable or inappropriate given the individual’s cultural and linguistic background. Use of 
these indicators is predicated on the clinician’s knowledge of and experience with typically developing individuals of comparable age. The behavioural indicators of intellectual 
functioning and adaptive behaviour functioning for each severity level are what are typically expected to be mastered by the individual as an adult. Please consult the CDDR for 
disorders of intellectual development and, if applicable, autism spectrum disorder for guidance on how to determine the severity level.
Neurodevelopmental disorders
Neurodevelopmental disorders | Disorders of intellectual development