Direct answer
Postorino, V. et al. · Developmental Services Ontario · Verified 2026-08-10
Quick summary
In brief
Key points
Prevalence and Assessment
The reported co-occurrence rate of intellectual disability in autism has changed over time as diagnostic practices have evolved.
Cognitive assessment in autistic individuals requires instruments validated for this population. Standard IQ tests may underestimate abilities due to the influence of language delays, social demands of the testing situation, and attentional differences. Ontario clinicians increasingly use non-verbal IQ measures (e.g., Leiter-3) and adaptive behaviour assessments (Vineland-3) to provide a more accurate picture.
Ontario Services for Dual ASD-ID
In Ontario, individuals with dual ASD-ID can access services through multiple pathways. The Ontario Autism Program provides clinical services during childhood. Developmental Services Ontario (DSO) provides the gateway to adult developmental services including residential supports, day programs, and Passport funding for community participation.
Eligibility for adult developmental services requires a Developmental Services Ontario application. Families often start before age 18 to reduce gaps. Confirm age rules, required assessments, and eligibility criteria with DSO.
The Surrey Place Dual Diagnosis Program in Toronto and regional dual diagnosis justice programs serve individuals with complex co-occurring presentations. Community Networks of Specialized Care provide consultation and support for challenging situations across Ontario.
Evidence and sources
Postorino, V. et al.
Intellectual Disability in Autism Spectrum Disorder: Investigation of Prevalence in an Italian Sample of Children and Adolescents. Research in Developmental Disabilities, 2016; 48:193-201
Developmental Services Ontario
Eligibility and application guidelines for adult developmental services, 2024
Frequently asked questions
- Does my child need a separate ID diagnosis to access developmental services?
- Developmental Services Ontario requires documentation of a developmental disability. An autism diagnosis alone may not qualify. Ask DSO what assessments are required and when to apply.
- What happens to services when my child with dual ASD-ID turns 18?
- At 18, Ontario Autism Program eligibility ends and adult supports may become the main pathway. Ask Developmental Services Ontario about Passport funding, residential support, and ODSP referrals.
- Can IQ tests accurately assess autistic children?
- Standard IQ tests may underestimate autistic children's abilities due to language demands, social testing conditions, and attentional differences. Request that the assessor use autism-appropriate instruments including non-verbal IQ measures and adaptive behaviour assessments. Multiple assessment sessions may be needed for accurate results.
Where the waitlist stands
Families navigating autism services in Ontario face a documented multi-year wait. Here is the Ontario data — and a two-minute way to push back, when you are ready.
About this page
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