Autism-pedia / Diagnosis / Diagnosis of autismbrianspringer.com
Diagnosis

Diagnosis of autism

An overview of how autism is diagnosed, who is missed and why, how recorded numbers have risen, how autism and ADHD overlap, and what a diagnosis changes. Each section links to a full entry.

A short tour of how autism gets diagnosed, who gets missed, and what changes after. Each part links to a longer page.

Last reviewed 12 October 2026 · one person's reading of the research · 26 sources

Assessment Established

Autism is diagnosed from behavior and developmental history.1 Most evidence on how accurate the standard tools are comes from children. In adults referred for assessment, questionnaires worked worse than in people already known to be autistic, and were especially poor at telling autism apart from mental-health conditions.2

Full entryAssessment How autism is diagnosed under DSM-5-TR and ICD-11, how accurate the standard tools and screening questionnaires are in children, adults and women, and how well clinicians agree.

Doctors diagnose autism by watching how a person acts and asking about their childhood.1 Most of the tools were tested on children. They work less well for adults.2

Full entryAssessment How doctors decide if someone is autistic, and how good their tests are.
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Established

Summarizes Assessment. A systematic review agrees that the tools work less well in adults referred for assessment than in children.

Established

Several studies agree. Most of the testing has been done with children.

Missed and late diagnosis Emerging

Across 56 studies from 40 countries, the average age at diagnosis was a little over 5 years, with very wide variation between studies.3 In studies that screened whole populations there were about 3 autistic boys for every girl, against about 4.6 in studies that counted only people already diagnosed, which suggests girls are missed more often.4 A 2007 survey of English households found about 1% of adults autistic, with no difference by age, and the autistic adults it found tended not to have been recognized.5

Full entryMissed and late diagnosis Who is diagnosed autistic late or not at all, what the research says about why, how the age at diagnosis has changed, and how adults come to be diagnosed.

On average, children are diagnosed when they are a little over 5 years old.3 Girls seem to be missed more often than boys.4 Some autistic adults have never been diagnosed at all.5

Full entryMissed and late diagnosis Some autistic people are found to be autistic late, or never. This page looks at who gets missed, why, and how adults find out.
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Emerging

Summarizes Missed and late diagnosis. The typical age comes from a meta-analysis; how many adults remain undiagnosed comes from single studies.

Emerging

The average age is well studied. The number of adults who were missed comes from single studies.

Rising prevalence Emerging

Recorded autism has risen steeply. In US surveillance of 8-year-olds, 1 in 152 met the definition in 2002 and 1 in 36 in 2020.6,7 In Swedish twins, autistic traits measured the same way stayed stable over ten years while registered diagnoses rose.8

Full entryRising prevalence How autism is counted, how far the numbers have risen in the US, the UK, Scandinavia and elsewhere, what the rise is made of, and what the few studies with a steady method say about whether the underlying rate has changed.

Many more children are diagnosed autistic now than 20 years ago.6,7 One study measured autistic traits the same way for ten years. The traits did not become more common, even though diagnoses rose.8

Full entryRising prevalence How scientists count autistic people, why the numbers have gone up so much, and what the best studies say about whether autism itself has become more common.
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Emerging

Summarizes Rising prevalence. The rise in recorded autism is well documented; whether autism itself has become more common is not settled.

Emerging

The rise in diagnoses is well measured. Whether autism itself is more common is not settled.

Autism and ADHD Established

Meta-analyses put ADHD in about 28 to 40% of autistic people, depending on who was sampled.9,10 In a US national survey, autistic children diagnosed with ADHD first received their autism diagnosis about 3 years later than others.11

Full entryAutism and ADHD together How often autism and ADHD occur in the same person, why the two could not be diagnosed together until 2013, what twin and gene studies show about shared roots, how one can hide the other at assessment, and what studies have found about people with both.

Many autistic people also have ADHD. Studies put it at about 3 or 4 in every 10.9,10 Kids who get an ADHD diagnosis first often get their autism diagnosis years later.11

Full entryAutism and ADHD together Many people are both autistic and have ADHD. This page is about how often that happens, why doctors could not give both labels until 2013, what twin and gene studies show, and how one can hide the other.
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Established

Summarizes Autism and ADHD together. Several meta-analyses agree on a large overlap, and two independent studies find the diagnostic delay.

Established

Several big reviews agree on this.

What diagnosis changes Established

Three systematic reviews found that a diagnosis in adulthood commonly brought relief and a new way of understanding past experiences.12,13,14 Many people also found the process confusing or disappointing, and went on reporting stigma and a lack of suitable support afterwards.12,13

Full entryWhat diagnosis changes What research shows about receiving an autism diagnosis as an adult. It covers relief and grief, identity and wellbeing, the words autistic people prefer, and what happens when they tell others. Most of the evidence comes from interviews and online surveys of self-selected adults, mostly white, speaking and without intellectual disability; children learning of their own diagnosis are not covered.

Many adults feel relief when they are diagnosed. It helps them make sense of their past.12,13,14 Some also find the process confusing, or feel they do not get enough help afterwards.12,13

Full entryWhat diagnosis changes What happens after someone finds out they are autistic, mostly as a grown-up. It covers feelings, how people see themselves, the words they like, and telling other people. Most of what we know comes from talking with people and from online surveys.
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Established

Summarizes What diagnosis changes. Three systematic reviews, mostly of interview studies, agree; they draw on many of the same studies.

Established

Several reviews agree. Most of the studies asked people about their experiences.

Support levels Emerging

DSM-5 added a severity rating to the autism diagnosis in 2013, with three levels: Level 1, "requiring support"; Level 2, "requiring substantial support"; and Level 3, "requiring very substantial support". A clinician rates social communication and restricted, repetitive behaviors separately.22,23,24 The manual adds that severity "may vary by context and fluctuate over time".25 In 81 school-aged children given a first diagnosis at Level 1, the average IQ was about 104, in the typical range, but the average adaptive score was about 77.26

Full entrySupport levels What DSM-5 Levels 1, 2 and 3 say, how clinicians choose one, how consistent the ratings are, what Level 1 does and does not tell you about a person's needs, and how ICD-11 handles the same question without levels. The research is almost all on children.

Since 2013, the doctors' rule book gives autism three levels. Level 1 means a person needs support. Level 2 means substantial support. Level 3 means very substantial support. Needs can change from place to place and over time. In one study, children diagnosed at Level 1 had typical scores on thinking tests. But their everyday skills scored much lower.

Full entrySupport levels Doctors who diagnose autism in the US can add a level, 1, 2 or 3. This page explains what the levels say, how doctors pick one, and why Level 1 does not mean "mild". Most of the research is about children.
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Emerging

Summarizes Support levels. The levels themselves are the manual's own wording; what Level 1 means in daily life rests on one clinic study of children.

Emerging

The levels come from the doctors' rule book. What Level 1 means day to day comes from one study.

Pathological demand avoidance Emerging

In 2003 Elizabeth Newson and her colleagues proposed that "pathological demand avoidance syndrome" be recognized as a separate entity within the pervasive developmental disorders, the umbrella group that then held autism and Asperger's syndrome.15 PDA is not in DSM-5 or ICD-11.16 A 2021 systematic review of 13 studies in children and adolescents found that all identified PDA from Newson's original descriptions; most relied only on parent report, and none asked people with PDA themselves.17 A 2026 systematic review of 12 studies rated every one at high risk of bias.18

Full entryPDA (pathological demand avoidance) PDA is a term for an intense, anxious avoidance of everyday demands, named by Elizabeth Newson and recast by many autistic people as a drive for autonomy. Where it came from, why it resonates, what the measures and studies show, and the arguments over the label.

In 2003 Elizabeth Newson and her colleagues said PDA should count as its own condition, separate from autism.15 The main diagnosis books used by doctors do not include PDA.16 A review of 13 studies found that most asked only parents. None asked people with PDA themselves.17 Another review found every study it checked had serious flaws.18

Full entryPDA (pathological demand avoidance) PDA is a name for a strong, anxious need to avoid everyday demands. Many autistic people call it a drive to be in charge of their own life. Where the name came from, what studies show, and why people argue about it.
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Emerging

Summarizes Pathological demand avoidance. Reviews by different groups agree the research is weak; whether PDA is a distinct profile is not settled.

Emerging

Reviews agree the research is weak. Whether PDA is its own thing is not settled.

Imposter syndrome and doubt Established

The psychologists Pauline Rose Clance and Suzanne Imes named the "impostor phenomenon" in 1978.19 In an Australian oral history study of 26 autistic adults diagnosed after 35, some said they at times questioned their own diagnostic status; one said "maybe I'm not autistic enough".20 In interviews with 12 UK adults diagnosed in adulthood about telling others, one subtheme was "Disbelief and Imposter Syndrome", and not being believed was common.21

Full entryImposter syndrome and doubt Some autistic people, after a diagnosis or self-identification, come to doubt they are really autistic. Where the idea of imposter feelings comes from, why it resonates, what small studies of late-diagnosed adults record, and the arguments it feeds.

Two psychologists named the idea of feeling like an impostor in 1978.19 In Australia, some adults diagnosed after age 35 said they sometimes questioned whether they were really autistic.20 In the UK, many adults diagnosed as grown-ups were not believed, and some felt like imposters.21

Full entryImposter syndrome and doubt Some autistic people start to doubt they are really autistic, even after a diagnosis that made sense. Where the idea of imposter feelings comes from, why it rings true for many writers, and what small studies have found.
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Established

Summarizes Imposter syndrome and doubt. Three small independent qualitative studies agree that some diagnosed adults describe this doubt; none measured how common it is.

Established

Three separate small studies agree that some diagnosed adults feel this. None counted how many.

Sources

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