Autism

Atypical Autism: What the Term Meant and Where It Stands Now

The ICD-10 category that no longer exists — what it meant, and what your diagnosis means now.

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Reviewed by Dr. Eva Lassey, PT, DPT · Last updated August 28, 2026

Atypical autism was a diagnosis in ICD-10, the World Health Organization's classification system3, for presentations that resembled autism but differed in age of onset or did not meet the full criteria. It was broadly the ICD equivalent of the DSM's PDD-NOS. ICD-11, effective 2022, removed it and folded these presentations into a single autism spectrum disorder diagnosis — matching the change the DSM-5 made in 2013. Existing diagnoses remain valid and no reassessment is required. If you were given this diagnosis, the current equivalent is autism spectrum disorder.

This term is no longer used in diagnosis. Atypical autism was removed in ICD-11, effective 2022. If you or your child received this diagnosis, it remains valid — no reassessment is required.

What it meant

ICD-10 listed atypical autism as a separate category from childhood autism. It applied where a presentation resembled autism but differed in one of two ways: onset appeared after the age of three, or the person did not show differences in all three areas the criteria required. In practice it functioned much as PDD-NOS did in the American system — the category for presentations that were clearly something, but didn't fit the criteria as written.

A note for readers outside the United States. ICD is the classification system used across most of the world, including the UK, Europe, and Australia. If you have an atypical autism diagnosis, it most likely came from an ICD-based assessment. American readers are more likely to have encountered PDD-NOS, which described a similar situation.

What changed

ICD-11 came into effect in 2022 and consolidated all previous autism subcategories3 — atypical autism, childhood autism, and Asperger's syndrome — into a single autism spectrum disorder diagnosis. It uses specifiers for intellectual functioning and language ability rather than separate categories. This aligned ICD with the DSM-5, which had made a comparable change in 20131, improving consistency in research and clinical practice internationally.

ICD-11 does list one thing the DSM-5 does not: loss of previously acquired skills, as a feature clinicians can use in making a diagnosis. Sensory features are in both manuals — the DSM-5 added hyper- or hyporeactivity to sensory input in 2013, and ICD-11 followed in 2022. Your diagnosis doesn't expire — existing diagnoses remain valid, and you don't need to be re-evaluated unless you want to, or unless a specific service requires a current-framework assessment.

Where sensory processing fits

Both current diagnostic manuals include sensory features in their autism criteria: the DSM-5 added hyper- or hyporeactivity to sensory input in 2013, and ICD-11, effective 2022, includes sensory processing differences too. Assessments carried out under older frameworks did not evaluate sensory processing, because it wasn't a criterion. For many people it is the most persistent daily factor, and it is a legitimate thing to raise with an occupational therapist.

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Atypical autism (PDD-NOS) resources

Frequently Asked Questions

Is atypical autism still a diagnosis?

No. It was removed in ICD-11, effective 2022, and folded into autism spectrum disorder. Existing diagnoses remain valid and no reassessment is required.

What is atypical autism called now?

Autism spectrum disorder. ICD-11 uses a single diagnosis with specifiers for intellectual functioning and language ability rather than separate subcategories.

Is atypical autism milder than autism?

No. It described presentations that differed in onset or didn't meet all the criteria as written — not presentations that were less significant. Someone with an atypical autism diagnosis may have substantial support needs.

Is atypical autism the same as PDD-NOS?

They served similar functions in different systems. Atypical autism was the ICD-10 category; PDD-NOS was the DSM-IV equivalent. Both covered presentations that didn't fit the other categories, and both were retired.

Do I need to be reassessed under ICD-11?

Not for the diagnosis itself — it remains valid and does not expire. A current-framework assessment is worth pursuing only where a specific service, school placement or benefit requires one, or where you want the sensory and support-need detail that older assessments generally did not record.

Does my diagnosis still stand?

Yes. Existing diagnoses remain valid and don't expire. Re-evaluation is only needed if you want it or if a specific service requires a current-framework assessment.

Sources

  1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). APA Publishing; May 2013.
  2. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR). APA Publishing; 2022.
  3. World Health Organization. ICD-11 for Mortality and Morbidity Statistics, 6A02 Autism spectrum disorder. Effective January 2022. Checked August 18, 2026.

Medical disclaimer. This page is for general educational purposes and does not constitute medical advice, diagnosis, or treatment. Diagnostic terminology changes over time; a diagnosis you or your child received remains valid. Always consult a qualified healthcare provider about your child.