What Is Autism Spectrum Disorder?
Autism Spectrum Disorder (ASD) is a neurodevelopmental condition recognized in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR). It is defined by two core domains: persistent differences in social communication and social interaction across multiple contexts; and restricted, repetitive patterns of behaviour, interests, or activities.
The term "spectrum" acknowledges that autism does not look the same in every person. It is not a linear continuum from "mild" to "severe", it is multidimensional. A person may have very high support needs in some areas (such as sensory regulation or daily living skills) while having exceptional abilities in others (such as pattern recognition, memory, or deep expertise in a specific subject).
In Canada, the Public Health Agency of Canada has summarized the 2019 Canadian Health Survey on Children and Youth as showing that about 1 in 50 children and youth aged 1 to 17 had an autism diagnosis. See our guide: What Is Autism?
The Three Levels of Autism
The DSM-5 specifies three levels of ASD, defined by the amount of support an individual requires. These levels are assessed at the time of diagnosis and may change over time as a person develops and their circumstances change.
Level 1
Requiring Support
Without support, notable difficulties in social communication are apparent. Initiating social interactions is challenging. Unusual or unsuccessful responses to social overtures of others may be observed. Inflexibility of behaviour causes significant interference in at least one context.
Level 2
Requiring Substantial Support
Marked deficits in verbal and non-verbal social communication skills. Social impairments are apparent even with support. Limited initiation of social interactions and reduced or atypical responses. Restricted/repetitive behaviours appear frequently enough to be obvious to casual observers.
Level 3
Very Substantial Support
Severe deficits in verbal and non-verbal social communication cause severe impairments in functioning. Very limited initiation of social interactions and minimal response to social overtures. Extreme difficulty coping with change; interferes with functioning in all spheres.
Ontario Context
89,799
children registered with OAP
77%
still waiting for core services
1 in 50
Canadian children have an ASD diagnosis (PHAC)
Source: MCCSS FOI · Mar 2026, Public Health Agency of Canada 2019 CHSCY
Common Co-Occurring Conditions
Many autistic people also have one or more co-occurring conditions. Research indicates that ADHD co-occurs with autism in approximately 30–80% of cases, depending on the study. Anxiety disorders are also extremely common, affecting the majority of autistic people at some point in their lives. Depression, obsessive-compulsive disorder (OCD), and intellectual disability are also frequently co-occurring.
Co-occurring conditions can complicate both diagnosis and treatment planning. When anxiety or ADHD is present alongside autism, symptoms can overlap in ways that require careful clinical differentiation. Having co-occurring conditions does not change an ASD diagnosis, but it does affect what supports and interventions are most appropriate.
In Ontario, a child's ASD diagnosis makes them eligible for the Ontario Autism Program regardless of their support level, subject to the program's current rules and registration requirements. Funding and service timing depend on the specific OAP stream and current program policies. Learn about OAP eligibility.
Autism Diagnosis in Canada
In Canada, an ASD diagnosis is made by a qualified health professional based on DSM-5-TR criteria. The assessment process typically involves a clinical interview, review of developmental history, standardized instruments such as the ADOS-2 (Autism Diagnostic Observation Schedule) and ADI-R (Autism Diagnostic Interview, Revised), and clinical observation of the individual.
In Ontario, the primary reason to pursue a formal ASD diagnosis for a child is to access the Ontario Autism Program (OAP), which provides government-funded therapy and support services. An ASD diagnosis is a mandatory requirement for OAP registration. Given that waitlist positions are typically based on registration date, families are advised to pursue diagnosis and register as early as possible.
For adults, an ASD diagnosis can unlock workplace accommodations, disability tax credits, and access to adult autism support programs, which vary by province. See our guide to getting an autism diagnosis in Ontario.
Frequently Asked Questions
What is autism spectrum disorder?
Autism Spectrum Disorder (ASD) is a neurodevelopmental condition characterized by differences in social communication and interaction, and restricted, repetitive patterns of behaviour, interests, or activities. It is diagnosed using the DSM-5-TR criteria and is called a "spectrum" because it manifests very differently across individuals.
What are the 3 levels of autism?
The DSM-5 defines three ASD support levels. Level 1 (requiring support): noticeable difficulties in social communication that impact daily life; repetitive behaviours cause some interference. Level 2 (requiring substantial support): marked deficits in verbal and non-verbal communication; significant challenges with social interaction. Level 3 (requiring very substantial support): severe deficits in social communication; very limited initiation and response to social overtures.
Is Asperger Syndrome still a diagnosis?
Since 2013, Asperger Syndrome is no longer a separate diagnosis in the DSM-5. People previously diagnosed with Asperger's would now receive an ASD Level 1 diagnosis. Many people who were diagnosed with Asperger Syndrome before 2013 continue to use the term as part of their identity, and some clinicians may still use it informally.
What does 'spectrum' mean in autism?
The 'spectrum' in autism spectrum disorder reflects the wide range of presentations, strengths, and support needs. Two people with ASD can look very different from each other, one may be non-speaking and require extensive support, while another may be highly verbal with a demanding career. The spectrum is not a linear scale from 'mild' to 'severe'; it is multidimensional.
How is ASD diagnosed in Canada?
ASD diagnosis in Canada requires a comprehensive assessment by a qualified professional: a psychologist, developmental paediatrician, or psychiatrist. The process includes developmental history, standardized assessment tools (such as ADOS-2 and ADI-R), and clinical observation. In Ontario, a formal ASD diagnosis is required to access the Ontario Autism Program and its associated funding.
Next Steps
Every Voice Matters. Every Letter Counts.
Ontario families assembled this evidence from the government’s own records. Put it to work.
