# 04 - 6A02 Autism spectrum disorder

# 6A02 Autism spectrum disorder

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Autism spectrum disorder
Essential (required) features
• Persistent deficits in initiating and sustaining social communication and reciprocal social 
interactions that are outside the expected range of typical functioning based on the 
individual’s age and level of intellectual development are required for diagnosis. Specific 
manifestations of these deficits vary according to chronological age, verbal and intellectual 
ability, and disorder severity. Manifestations may include limitations in the following:
• understanding of, interest in, or inappropriate responses to the verbal or nonverbal social 
communications of others;
• integration of spoken language with typical complimentary nonverbal cues, such as eye 
contact, gestures, facial expressions and body language (these nonverbal behaviours may 
also be reduced in frequency or intensity);
• understanding and use of language in social contexts and ability to initiate and sustain 
reciprocal social conversations;
• social awareness, leading to behaviour that is not appropriately modulated according to 
the social context;
• ability to imagine and respond to the feelings, emotional states and attitudes of others;
• mutual sharing of interests;
• ability to make and sustain typical peer relationships.
• Persistent restricted, repetitive and inflexible patterns of behaviour, interests or activities 
that are clearly atypical or excessive for the individual’s age and sociocultural context are 
an essential component. These may include:
• lack of adaptability to new experiences and circumstances, with associated distress, that 
can be evoked by trivial changes to a familiar environment or in response to unanticipated 
events;
• inflexible adherence to particular routines – for example, these may be geographical, such 
as following familiar routes, or may require precise timing such as mealtimes or transport;
• excessive adherence to rules (e.g. when playing games);
• excessive and persistent ritualized patterns of behaviour (e.g. preoccupation with lining 
up or sorting objects in a particular way) that serve no apparent external purpose;
• repetitive and stereotyped motor movements such as whole-body movements (e.g. 
rocking), atypical gait (e.g. walking on tiptoes), unusual hand or finger movements and 
posturing (these behaviours are particularly common during early childhood);
• persistent preoccupation with one or more special interests, parts of objects or specific 
types of stimuli (including media), or an unusually strong attachment to particular objects 
(excluding typical comforters);
• lifelong excessive and persistent hypersensitivity or hyposensitivity to sensory stimuli or 
unusual interest in a sensory stimulus, which may include actual or anticipated sounds, 
light, textures (especially clothing and food), odours and tastes, heat, cold or pain.
• The onset of the disorder occurs during the developmental period – typically in early 
childhood – but characteristic symptoms may not become fully manifest until later, when 
social demands exceed limited capacities.
6A02
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Neurodevelopmental disorders
• The symptoms result in significant impairment in personal, family, social, educational, 
occupational or other important areas of functioning. Some individuals with autism 
spectrum disorder are able to function adequately in many contexts through exceptional 
effort, such that their deficits may not be apparent to others. A diagnosis of autism spectrum 
disorder is still appropriate in such cases.
Specifiers for characterizing features within the autism spectrum
These specifiers enable the identification of co-occurring limitations in intellectual and functional 
language abilities, which are important factors in the appropriate individualization of support, 
selection of interventions and treatment planning for individuals with autism spectrum disorder. A 
specifier is also provided for loss of previously acquired skills, which is a feature of the developmental 
history of a small proportion of individuals with autism spectrum disorder.
Co-occurring disorder of intellectual development
Individuals with autism spectrum disorder may exhibit limitations in intellectual abilities. If present, 
a separate diagnosis of disorder of intellectual development should be assigned, using the appropriate 
category to designate severity (i.e. mild, moderate, severe, profound, provisional). Because social 
deficits are a core feature of autism spectrum disorder, the assessment of adaptive behaviour as a part 
of the diagnosis of a co-occurring disorder of intellectual development should place greater emphasis 
on the intellectual, conceptual and practical domains of adaptive functioning than on social skills.
If no co-occurring diagnosis of disorder of intellectual development is present, the following specifier 
for the autism spectrum disorder diagnosis should be applied:
• without disorder of intellectual development.
If there is a co-occurring diagnosis of disorder of intellectual development, the following specifier for 
the autism spectrum disorder diagnosis should be applied, in addition to the appropriate diagnostic 
code for the co-occurring disorder of intellectual development:
• with disorder of intellectual development.
Degree of functional language impairment
The degree of impairment in functional language (spoken or signed) should be designated with a 
second specifier. Functional language refers to the capacity of the individual to use language for 
instrumental purposes (e.g. to express personal needs and desires). This specifier is intended to 
reflect primarily the verbal and nonverbal expressive language deficits present in some individuals 
with autism spectrum disorder, and not the pragmatic language deficits that are a core feature of 
autism spectrum disorder.
Neurodevelopmental disorders | Autism spectrum disorder

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
The following specifiers should be applied to indicate the extent of functional language impairment 
(spoken or signed) relative to the individual’s age:
• with mild or no impairment of functional language
• with impaired functional language (i.e. not able to use more than single words or simple 
phrases)
• with complete, or almost complete, absence of functional language.
Table 6.5 shows the diagnostic codes corresponding to the categories that result from the application 
of the specifiers for co-occurring disorder of intellectual development and degree of functional 
language impairment.
Table 6.5. Diagnostic codes for autism spectrum disorder
With mild or no 
impairment of 
functional language
With impaired 
functional language
With complete, or 
almost complete, 
absence of functional 
language
Without disorder of 
intellectual development
6A02.0
6A02.2
_____
With disorder of intellectual 
development
6A02.1
6A02.3
6A02.5
6A02.Y Other specified autism spectrum disorder can be used if the above parameters do not 
apply.
6A02.Z Autism spectrum disorder, unspecified, can be used if the above parameters are unknown.
Loss of previously acquired skills
A small proportion of individuals with autism spectrum disorder may present with a loss of 
previously acquired skills. This regression typically occurs during the second year of life and most 
often involves language use and social responsiveness. Loss of previously acquired skills is rarely 
observed after 3 years of age. If it occurs after age 3, it is more likely to involve loss of cognitive and 
adaptive skills (e.g. loss of bowel and bladder control, impaired sleep), regression of language and 
social abilities, and increasing emotional and behavioural disturbances.
There are two alternative specifiers to denote whether or not loss of previously acquired skills is an 
aspect of the clinical history, where x corresponds to the final digit shown in Table 6.5:
• 6A02.x0 without loss of previously acquired skills
• 6A02.x1 with loss of previously acquired skills.
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Additional clinical features
• Common symptom presentations of autism spectrum disorder in young children are 
parental or caregiver concerns about intellectual or other developmental delays (e.g. 
problems in language and motor coordination). When there is no significant impairment 
of intellectual functioning, clinical services may only be sought later (e.g. due to behaviour 
or social problems when starting school). In middle childhood, there may be prominent 
symptoms of anxiety, including social anxiety disorder, school refusal and specific phobia. 
During adolescence and adulthood, depressive disorders are often a presenting feature.
• Co-occurrence of autism spectrum disorder with other mental, behavioural and 
neurodevelopmental disorders is common across the lifespan. In a substantial proportion 
of cases – particularly in adolescence and adulthood – it is a co-occurring disorder that 
first brings an individual with autism spectrum disorder to clinical attention.
• Pragmatic language difficulties may manifest as an overly literal understanding of others’ 
speech, speech that lacks normal prosody and emotional tone and therefore appears 
monotonous, lack of awareness of the appropriateness of their choice of language in 
particular social contexts, or pedantic precision in the use of language.
• Social naivety, especially during adolescence, can lead to exploitation by others – a risk that 
may be enhanced by the use of social media without adequate supervision.
• Profiles of specific cognitive skills in autism spectrum disorder as measured by standardized 
assessments may show striking and unusual patterns of strengths and weaknesses that 
are highly variable from individual to individual. These deficits can affect learning and 
adaptive functioning to a greater extent than would be predicted from the overall scores 
on measures of verbal and nonverbal intelligence.
• Self-injurious behaviours (e.g. hitting one’s face, head banging) occur more often in 
individuals with co-occurring disorder of intellectual development.
• Some young individuals with autism spectrum disorder – especially those with a cooccurring disorder of intellectual development – develop epilepsy or seizures during 
early childhood with a second increase in prevalence during adolescence. Catatonic states 
have also been described. A number of medical disorders such as tuberous sclerosis, 
chromosomal abnormalities including fragile X syndrome, cerebral palsy, early-onset 
epileptic encephalopathies and neurofibromatosis are associated with autism spectrum 
disorder with or without a co-occurring disorder of intellectual development. Genomic 
deletions, duplications and other genetic abnormalities are increasingly described in 
individuals with autism spectrum disorder, some of which may be important for genetic 
counselling. Prenatal exposure to valproate is also associated with an increased risk of 
autism spectrum disorder.
• Some individuals with autism spectrum disorder are capable of functioning adequately 
by making an exceptional effort to compensate for their symptoms during childhood, 
adolescence or adulthood. Such sustained effort, which may be more typical of affected 
females, can have a deleterious impact on mental health and well-being.
Neurodevelopmental disorders | Autism spectrum disorder

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Boundary with normality (threshold)
Social interaction skills
Typically developing individuals vary in the pace and extent to which they acquire and master skills 
of reciprocal social interaction and social communication. A diagnosis of autism spectrum disorder 
should only be considered if there is marked and persistent deviation from the expected range of 
abilities and behaviours in these domains given the individual’s age, level of intellectual functioning 
and sociocultural context. Some individuals may exhibit limited social interaction due to shyness 
(i.e. feelings of awkwardness or fear in new situations or with unfamiliar people) or behavioural 
inhibition (i.e. being slow to approach or to “warm up” to new people and situations). Limited social 
interactions in shy or behaviourally inhibited children, adolescents or adults are not indicative of 
autism spectrum disorder. Shyness is differentiated from autism spectrum disorder by evidence of 
adequate social communication behaviours in familiar situations.
Social communication skills
Children vary widely in the age at which they first acquire spoken language and the pace at which 
their speech and language become firmly established. Most children with early language delay 
eventually acquire similar language skills to those of their same-age peers. Early language delay 
alone is not strongly indicative of autism spectrum disorder unless there is also evidence of 
limited motivation for social communication and limited interaction skills. An essential feature of 
autism spectrum disorder is persistent impairment in the ability to understand and use language 
appropriately for social communication.
Repetitive and stereotyped behaviours
Many children go through phases of repetitive play and highly focused interests as a part of typical 
development. Unless there is also evidence of impaired reciprocal social interaction and social 
communication, patterns of behaviour characterized by repetition, routine or restricted interests 
are not by themselves indicative of autism spectrum disorder.
Course features
• Although autism spectrum disorder can present clinically at all ages, including during 
adulthood, it is a lifelong disorder, the manifestations and impact of which are likely to 
vary according to age, intellectual and language abilities, co-occurring conditions and 
environmental context.
• Restricted and repetitive behaviours persist over time. Specifically, repetitive sensorimotor 
behaviours appear to be common, consistent and potentially severe. During the schoolage years and adolescence, these repetitive sensorimotor behaviours begin to lessen in 
intensity and number. Insistence on sameness, which is less prevalent, appears to develop 
during preschool and worsen over time.
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Developmental presentations
Infancy
Characteristic features may emerge during infancy, although they may only be recognized as 
indicative of autism spectrum disorder in retrospect. It is usually possible to make the diagnosis of 
autism spectrum disorder during the preschool period (up to 4 years of age), especially in children 
exhibiting generalized developmental delay. Plateauing of social communication and language skills 
and failure to progress in their development is not uncommon. The loss of early words and social 
responsiveness – i.e. a true regression – with an onset between 1 and 2 years of age is unusual but 
significant, and rarely occurs after the third year of life. In these cases, the with loss of previously 
acquired skills specifier should be applied.
Preschool
In preschool-aged children, indicators of an autism spectrum disorder diagnosis often include 
avoidance of mutual eye contact, resistance to physical affection, a lack of social imaginary play, 
language that is delayed in onset or is precocious but not used for social conversation; social 
withdrawal, obsessive or repetitive preoccupations, and a lack of social interaction with peers 
characterized by parallel play or disinterest. Sensory sensitivities to everyday sounds, or to foods, 
may overshadow the underlying social communication deficits.
Middle childhood
In children with autism spectrum disorder without a disorder of intellectual development, social 
adjustment difficulties outside the home may not be detected until middle childhood (commonly at 
school entry) or during adolescence, when social communication problems lead to social isolation 
from peers. Resistance to engage in unfamiliar experiences and marked reactions to even minor 
change in routines are typical. Furthermore, excessive focus on detail and rigidity of behaviour and 
thinking may be significant. Symptoms of anxiety may become evident at this stage of development.
Adolescence
By adolescence, the capacity to cope with increasing social complexity in peer relationships at a time 
of increasingly demanding academic expectations is often overwhelmed. In some individuals with 
autism spectrum disorder, the underlying social communication deficits may be overshadowed by 
the symptoms of co-occurring mental and behavioural disorders. Depressive symptoms are often 
a presenting feature.
Adulthood
In adulthood, the capacity for those with autism spectrum disorder to cope with social relationships 
can become increasingly challenged, and clinical presentation may occur when social demands 
overwhelm the capacity to compensate. Presenting problems in adulthood may represent reactions 
to social isolation or the social consequences of inappropriate behaviour. Compensation strategies 
may be sufficient to sustain dyadic relationships, but are usually inadequate in social groups. Special 
interests, and focused attention, may benefit some individuals in education and employment. 
Work environments may have to be tailored to the capacities of the individual. A first diagnosis 
in adulthood may be precipitated by a breakdown in domestic or work relationships. In autism 
spectrum disorder there is always a history of early childhood social communication and relationship 
difficulties, although this may only be apparent in retrospect.
Neurodevelopmental disorders | Autism spectrum disorder

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Culture-related features
• Cultural variation exists in norms of social communication and reciprocal social 
interactions, as well as interests and activities. Therefore, signs of impairment in 
functioning may differ depending on cultural context. For example, in some societies it 
may be normative for children may avoid direct eye contact out of deference, which should 
not be misinterpreted as impairment in social interaction.
Sex- and/or gender-related features
• Males are four times more likely than females to be diagnosed with autism spectrum disorder.
• Females diagnosed with autism spectrum disorder are more frequently diagnosed with 
co-occurring disorders of intellectual development than males, suggesting that less severe 
presentations may go undetected. Females tend to demonstrate fewer restricted, repetitive 
interests and behaviours.
• During middle childhood, gender differences in presentation differentially affect 
functioning. Boys may act out with reactive aggression or other behavioural symptoms 
when challenged or frustrated. Girls tend to withdraw socially, and react with emotional 
changes to their social adjustment difficulties.
Boundaries with other disorders and conditions (differential diagnosis)
Boundary with disorders of intellectual development
Autism spectrum disorder may be diagnosed in individuals with disorders of intellectual 
development if deficits in initiating and sustaining social communication and reciprocal social 
interactions are greater than would be expected based on the individual’s level of intellectual 
functioning, and if the other diagnostic requirements for autism spectrum disorder are also met. 
In these circumstances, both autism spectrum disorder and the disorder of intellectual development 
should be assigned, and the with disorder of intellectual development specifier should be applied with 
the autism spectrum disorder diagnosis. 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 intellectual functioning and the 
conceptual and practical domains of adaptive functioning than on social skills. 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. However, 
the diagnosis may be assigned if skills in social reciprocity and communication are significantly 
impaired relative to the individual’s general level of intellectual ability.
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Boundary with developmental language disorder with impairment of mainly 
pragmatic language
Individuals with developmental language disorder with impairment of mainly pragmatic language 
exhibit language deficits involving the ability to understand and use language in social contexts (i.e. 
with pragmatic language impairment). Unlike individuals with autism spectrum disorder, individuals 
with developmental language disorder are usually able to initiate and respond appropriately to 
social and emotional cues and to share interests with others, and do not typically exhibit restricted, 
repetitive and stereotyped behaviours. An additional diagnosis of developmental language disorder 
should not be assigned to individuals with autism spectrum disorder based solely on pragmatic 
language impairment. The other forms of developmental language disorder (i.e. with impairment 
of receptive and expressive language or with impairment of receptive and expressive language) may 
be assigned in conjunction with a diagnosis of autism spectrum disorder if language abilities are 
markedly below what would be expected based on age and level of intellectual functioning.
Boundary with developmental motor coordination disorder
Individuals with autism spectrum disorder may be reluctant to participate in tasks requiring 
complex motor coordination skills, such as ball sports, which is better accounted for by a lack of 
interest rather than any specific deficits in motor coordination. However, developmental motor 
coordination disorder and autism spectrum disorder can co-occur, and both diagnoses may be 
assigned if warranted.
Boundary with attention deficit hyperactivity disorder
Specific abnormalities in attention (e.g. being overly focused or easily distracted), impulsivity 
and physical hyperactivity are often observed in individuals with autism spectrum disorder. 
However, individuals with attention deficit hyperactivity disorder do not exhibit the persistent 
deficits in initiating and sustaining social communication and reciprocal social interactions or 
the persistent restricted, repetitive and inflexible patterns of behaviour, interests or activities that 
are the defining features of autism spectrum disorder. However, autism spectrum disorder and 
attention deficit hyperactivity disorder can co-occur, and both diagnoses may be assigned if the 
diagnostic requirements for each are met. Attention deficit hyperactivity disorder symptoms may 
sometimes dominate the clinical presentation such that some autism spectrum disorder symptoms 
are less apparent.
Boundary with stereotyped movement disorder
Stereotyped movement disorder is characterized by voluntary, repetitive, stereotyped, apparently 
purposeless (and often rhythmic) movements that arise during the early developmental period. 
Although such stereotyped movements are typical in autism spectrum disorder, if they are severe 
enough to require additional clinical attention – for example, because of self-injury – a co-occurring 
diagnosis of stereotyped movement disorder may be warranted.
Boundary with schizophrenia
The onset of schizophrenia may be associated with prominent social withdrawal, which is either 
preceded by or results in social impairments that may resemble social deficits seen in autism 
spectrum disorder. However, unlike autism spectrum disorder, the onset of schizophrenia is 
typically in adolescence or early adulthood, and is extremely rare prior to puberty. Schizophrenia 
is differentiated on the basis of the presence of psychotic symptoms (e.g. delusions, hallucinations), 
as well as a lack of restricted, repetitive and inflexible patterns of behaviour, interests or activities 
during early childhood typical of autism spectrum disorder.
Boundary with schizotypal disorder
Interpersonal difficulties seen in autism spectrum disorder may share some features of schizotypal 
disorder, such as poor rapport with others and social withdrawal. However, autism spectrum 
disorder is also characterized by restricted, repetitive and stereotyped patterns of behaviour, interests 
or activities.
Neurodevelopmental disorders | Autism spectrum disorder

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
Boundary with social anxiety disorder
Social anxiety disorder is associated with limited engagement in social interaction due to marked 
and excessive fear or anxiety about negatively evaluated by others. Typically, when interacting with 
familiar others or in social situations that do not provoke significant anxiety, there is no evidence 
of impairment. Individuals with autism spectrum disorder may experience social anxiety, but 
they also exhibit more pervasive deficits in initiating and sustaining social communication and 
reciprocal social interactions than are typically observed in social anxiety disorder. Persistent 
restricted, repetitive and inflexible patterns of behaviour, interests or activities are not features of 
social anxiety disorder.
Boundary with selective mutism
Selective mutism is characterized by normal use of language and patterns of social communication in 
specific environments (such as the home), but not in others (such as at school). In autism spectrum 
disorder, a reluctance to communicate may be observed in some social circumstances, but deficits 
in initiating and sustaining social communication and reciprocal social interactions and persistent 
restricted, repetitive and inflexible patterns of behaviour, interests or activities are evident across 
all situations and contexts.
Boundary with obsessive-compulsive disorder
Obsessive-compulsive disorder is characterized by persistent repetitive thoughts, images, or 
impulses/urges (i.e. obsessions) and/or repetitive behaviours (i.e. compulsions) that the individual 
feels driven to perform in response to an obsession, according to rigid rules, to reduce anxiety or to 
achieve a sense of “completeness”. These symptoms may be difficult to distinguish from restricted, 
repetitive and inflexible patterns of behaviour, interests or activities that are characteristic of autism 
spectrum disorder. Unlike those with autism spectrum disorder, it is more common for individuals 
with obsessive-compulsive disorder consciously to resist their impulsive urges to perform compulsive 
behaviours (e.g. by performing alternate tasks), though adolescents and adults with autism spectrum 
disorder may also try to suppress specific behaviours that they realize are socially undesirable. 
Autism spectrum disorder can also be distinguished from obsessive-compulsive disorder by its 
characteristic deficits in initiating and sustaining social communication and reciprocal social 
interactions, which are not features of obsessive-compulsive disorder.
Boundary with reactive attachment disorder
Reactive attachment disorder is characterized by inhibited emotionally withdrawn behaviour 
exhibited towards adult caregivers, including a failure to approach a discriminated, preferred 
attachment figure for comfort, support, protection or nurturance. The diagnosis of reactive 
attachment disorder requires evidence of a history of severe neglect or maltreatment by the primary 
caregiver or other forms of severe social deprivation (e.g. certain types of institutionalization). Some 
individuals reared under conditions of severe deprivation in institutional settings exhibit autistic-like 
features, including difficulties in social reciprocity and restricted, repetitive and inflexible patterns 
of behaviour, interests or activities. Also referred to as “quasi-autism”, affected individuals are 
differentiated from those with autism spectrum disorder based on significant improvement of 
autism-like features when the child is moved to a more nurturing environment. Differentiation 
between reactive attachment disorder and autism spectrum disorder is difficult when no reliable 
evidence is available of intact social and communicative development prior to the onset of abuse 
or neglect.
Boundary with disinhibited social engagement disorder
Disinhibited social engagement disorder is characterized by persistent indiscriminate social 
approaches to unfamiliar adults and peers, a pattern of behaviour that may also be seen in some 
children with autism spectrum disorder. The diagnosis of disinhibited social engagement disorder 
requires evidence of a history of severe neglect or maltreatment by the primary caregiver or other 
forms of severe social deprivation (e.g. certain types of institutionalization). As in reactive attachment 
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disorder, disinhibited social engagement disorder may be associated with generalized deficits in 
social understanding and social communication. Although they may occur, restricted, repetitive 
and inflexible patterns of behaviour, interests or activities are not typical features of disinhibited 
social engagement disorder. Evidence of a significant reduction in symptoms when the child is 
provided a more nurturing environment suggests that disinhibited social engagement disorder is 
the appropriate diagnosis.
Boundary with avoidant-restrictive food intake disorder
Individuals with avoidant-restrictive food intake disorder sometimes restrict their food intake 
based on food’s sensory characteristics such as smell, taste, temperature, texture or appearance. 
Individuals with autism spectrum disorder may also restrict intake of certain foods because of their 
sensory characteristics or because of inflexible adherence to particular routines. However, autism 
spectrum disorder is also characterized by persistent deficits in initiating and sustaining social 
communication and reciprocal social interactions and persistent restricted, repetitive and inflexible 
patterns of behaviour, interests or activities that are unrelated to food. If a pattern of restricted eating 
in an individual with autism spectrum disorder has caused significant weight loss or other health 
consequences, or is specifically associated with significant functional impairment, an additional 
diagnosis of avoidant-restrictive food intake disorder may be assigned.
Boundary with oppositional defiant disorder
Oppositional defiant disorder is characterized by a pattern of markedly noncompliant, defiant 
and disobedient disruptive behaviour that is not typical for individuals of comparable age and 
developmental level. Individuals with oppositional defiant disorder do not exhibit the social 
communication deficits or restricted, repetitive and inflexible patterns of behaviour, interests or 
activities that are characteristic of autism spectrum disorder. However, oppositional or “demand 
avoidant” behaviour may be prominent in some children with autism spectrum disorder, whether or 
not they have accompanying intellectual or functional language impairments, and may sometimes be 
the presenting feature in school-aged children with autism spectrum disorder. Disruptive behaviour 
with aggressive outbursts (explosive rages) may also be a prominent feature of autism spectrum 
disorder. Among individuals with autism spectrum disorder, such outbursts are often associated 
with a specific trigger (e.g. a change in routine, aversive sensory stimulation, anxiety or rigidity 
when the individual’s thoughts or behaviour sequences are interrupted) rather than reflecting an 
intention to be defiant, provocative or spiteful, as is more typical of oppositional defiant disorder.
Boundary with personality disorder
Personality disorder is a pervasive disturbance in how an individual experiences and thinks about the 
self, others and the world, manifested in maladaptive patterns of cognition, emotional experience, 
emotional expression and behaviour. The maladaptive patterns are relatively inflexible, manifesting 
across a range of personal and social situations; relatively stable over time; and of long duration. They 
are associated with significant problems in psychosocial functioning that are particularly evident in 
interpersonal relationships. The difficulties some individuals with autism spectrum disorder exhibit 
in initiating and maintaining relationships because of their limited skills in social communication 
and reciprocal social interactions may resemble those seen in some individuals with personality 
disorder. However, unlike autism spectrum disorder, persistent restricted, repetitive and inflexible 
patterns of behaviour, interests or activities with onset in early childhood are not characteristic 
features of personality disorder. 
Boundary with primary tics and tic disorders including Tourette syndrome
Sudden, rapid, non-rhythmic and recurrent movements or vocalizations occur in primary tics and 
tic disorders, which may resemble repetitive and stereotyped motor movements in autism spectrum 
disorder. Unlike autism spectrum disorder, tics in primary tics and tic disorders tend to be less 
stereotyped, are often accompanied by premonitory sensory urges, last for a shorter period, tend 
to emerge later in life, and are not experienced by the individual as soothing.
Neurodevelopmental disorders | Autism spectrum disorder