Re-Diagnosis of Autism: When Diagnostic Criteria Change
Direct answer
Ontario asks for a written diagnosis of autism from a qualified professional, with a statement that the child meets the diagnostic criteria for autism spectrum disorder. AccessOAP decides whether an older DSM-IV letter (such as Asperger syndrome or PDD-NOS) meets that requirement, so call AccessOAP (1-833-425-2445) before booking a new assessment. However, individuals diagnosed with Asperger syndrome or PDD-NOS may choose to seek updated assessment for personal or employment accommodation purposes. Ask private providers for a written fee quote.
Why Timing Matters
The wait outlasts the window.
Clinical research (American Academy of Pediatrics; Hyman et al., Pediatrics 2020) identifies birth to age six as the peak neuroplasticity window for autism intervention. Ontario's reported minimum wait is 5+ years for families registered in August 2021 (community-reported, Ontario Autism Coalition, July 2026).
Example: an illustrative child's journey through the Ontario Autism Program
Registered at age 3. Services begin at age 8, after 5+ years for families registered in August 2021 (community-reported, Ontario Autism Coalition, July 2026), most of it inside the intervention window.
| Measure | Age range |
|---|---|
| Early-intervention window (AAP) | Birth to age 6 |
| Example wait using the OAC-reported minimum (registered age 3) | Age 3 to age 8 (5 years) |
| Age when services begin in this example | Past age 6 |
✓ Intervention before 6
Research shows 2× greater gains in cognitive and adaptive functioning. Some children lose their diagnosis entirely. The brain's plasticity makes early therapy dramatically more effective.
◌ Intervention after 6
Reduced neuroplasticity means slower progress, higher lifetime costs, and poorer outcomes. Every year of delay narrows the range of achievable milestones. Ontario's waitlist guarantees this for most families.
Of the 71,263 children on the unfunded backlog, the majority were registered between ages 2 and 4. At the current pace, most will age past 6 before receiving any core funding , missing the window that the American Academy of Pediatrics and every major autism research body identifies as critical.
SourceAmerican Academy of Pediatrics (Hyman et al., Pediatrics 2020) · Ontario MCCSS OAP data via FOI · Wait: 5+ years for families registered in August 2021 (community-reported, Ontario Autism Coalition, July 2026).
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What Changed in DSM-5
- The DSM-5 (2013) merged four previously separate diagnoses — autistic disorder, Asperger syndrome, PDD-NOS, and childhood disintegrative disorder — into a single Autism Spectrum Disorder (ASD) diagnosis with severity levels 1-3. The two-domain criteria (social communication + restricted/repetitive behaviours) replaced the three-domain model. Sensory differences were added as a diagnostic feature.
Ontario's Approach to Prior Diagnoses
- Ontario asks for a written diagnosis of autism from a qualified professional, with a statement that the child meets the diagnostic criteria for autism spectrum disorder. AccessOAP decides whether an older diagnosis of Asperger syndrome, PDD-NOS or childhood disintegrative disorder meets that requirement. Call AccessOAP before booking a new assessment.
- Reasons to consider voluntary re-assessment include: wanting a formal DSM-5 diagnosis for clarity, needing updated documentation for workplace accommodations, needing current health information for an ODSP application, or wanting a comprehensive assessment that identifies co-occurring conditions (ADHD, anxiety, learning disabilities) that were not assessed previously.
Frequently asked questions
Ontario asks for a written diagnosis that states the child meets the diagnostic criteria for autism spectrum disorder. AccessOAP decides whether an older letter meets that requirement, so call AccessOAP (1-833-425-2445) before booking a new assessment.
Asperger syndrome was removed as a separate diagnosis in the DSM-5 (2013) and folded into Autism Spectrum Disorder. Under DSM-5, people with a well-established Asperger diagnosis should be given a diagnosis of autism spectrum disorder. Many individuals continue to identify with the term. For the OAP, AccessOAP decides whether an older Asperger letter meets current requirements.
DSM-5 says people with a well-established DSM-IV diagnosis of autistic disorder, Asperger’s disorder or PDD-NOS should be given a diagnosis of autism spectrum disorder. For the OAP, ask AccessOAP whether your older letter meets current requirements. If you choose to be reassessed, ask the clinician how the new assessment would relate to your earlier diagnosis.
Sources
APA
American Psychiatric Association — DSM-5 Autism Spectrum Disorder Fact Sheet (2013)
Ontario Autism Program — Eligibility (ontario.ca, updated April 16, 2026)
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Next step near you
Where to be assessed near you
- TorontoHolland Bloorview
- OttawaCHEO
- MississaugaErinoakKids (Mississauga Facility)
- BramptonErinoakKids (Brampton)
- North YorkHolland Bloorview (referral)
- ScarboroughSickKids (referral)
See every Ontario city we track
Assessment routes, local providers and school boards are tracked city by city. Pick the one closest to you.
Where the wait clock starts
A child's place in the Ontario Autism Program queue is set by the AccessOAP registration date. 71,263 children are registered and still waiting for core funding (MCCSS FOI via OAC · May 2026).
Next steps
Keep going with related guidance, tools, and evidence.
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