What is autism?

The two core areas

The World Health Organization’s international classification (ICD-11) describes autism through two areas: ^[1]

1. Social communication and interaction. People with autism have persistent difficulty starting and sustaining reciprocal social contact and conversations. ^[1] As examples, the account of the DSM-5 criteria (not the ICD-11 wording) gives: ^[2]

• Eye contact, facial expression and gestures are used or read differently.
• It is harder to build and keep friendships.

2. Repetitive, restricted and inflexible patterns of behaviour, interests or activities that are clearly unusual or pronounced for the person’s age and social setting. ^[1] As examples, the account of the DSM-5 criteria gives: ^[2]

• Holding on to routines and difficulty with change.
• Very intense or fixed interests.
• Repeated movements or actions (stereotypies).
• Over- or under-reaction to sensory stimuli.

Not every person with autism shows all of these examples. According to the expert overview, similar features also occur in other disorders. ^[2] For a diagnosis, what matters is that they occur together, persistently and in different areas of life. ^[2]

Why we speak of a spectrum

The forms that used to be separate, such as “early childhood autism”, “Asperger syndrome” or “atypical autism”, are combined in the ICD-11 and in the American diagnostic manual DSM-5 under the single diagnosis autism spectrum disorder. ^[2] In Germany, ICD-10-GM is so far the official classification for diagnoses in outpatient and inpatient care. According to the Federal Institute for Drugs and Medical Devices (BfArM), it remains valid until ICD-11 is introduced; introducing ICD-11 for diagnosis coding will take several more years. ^[7] Older diagnosis names may therefore appear in reports and documents.

Instead, the ICD-11 describes the differences between people on the autism spectrum through two additional specifications: ^[1]

• whether an intellectual disability is also present or not,
• how well someone can use language functionally, that is, to express needs and communicate.

This shows how wide the range is: in the ICD-11, functional language ranges all the way to an absence of functional language. ^[1] More on this in the article The autism spectrum.

When autism becomes apparent

Autism begins during the developmental period, typically in early childhood. The ICD-11 stresses, however, that the features sometimes only become clear later, when social demands exceed a person’s abilities. ^[1] This is one possible reason why some people only receive a diagnosis in adolescence or adulthood. This article does not cover further reasons.

How autism is diagnosed

Autism is diagnosed clinically by professionals, that is, on the basis of conversations, developmental history and observation. There are so far no specific biological markers, such as a laboratory test, for this. ^[3] A typical route looks like this: ^[3]

• First comes an assessment in a specialist practice or outpatient clinic, for example through a history, observation and questionnaires.
• For children, assessment of development, language and intelligence is part of it.
• A physical examination also takes place.
• If the suspicion is confirmed, a comprehensive work-up with standardised methods follows.

It is always important, too, to distinguish autism from other explanations for the difficulties observed. ^[3]

How this works in practice is explained in the article How an autism assessment works.

How common autism is

A systematic review summarised 99 estimates from 71 studies published since 2012. The median of the estimates was 100 per 10,000 (about 1%); individual estimates ranged from 1.09 to 436 per 10,000, and the regional medians from 23 to 205 per 10,000. The studies mostly come from wealthy countries. ^[6] The article How common is autism? explains the details and limits of these figures.

What the 2021 S3 guideline said about support

The German S3 guideline on therapy from 2021 stated: a diagnosis of autism does not automatically mean that ongoing therapy is needed. Where support is useful, it should be guided by specific, jointly agreed goals. The overarching aim is a better quality of life and participation, that is, the opportunity to take part in social life. This was a consensus-based recommendation, not a statement drawn from studies of effectiveness. ^{[4, Empfehlung 1]}

For everyday dealings with people with autism, the guideline also named points that can be helpful, each adapted to the individual person (likewise a consensus-based recommendation): ^{[4, Empfehlung 3]}

• concrete, direct language,
• clear structures and predictability, for example through visual aids,
• as far as possible, consistent people to turn to,
• consideration for physical distance,
• avoiding strong sensory stimuli such as noise, smells or bright light.

You might also be interested in

• How an autism assessment works

Sources and literature

1. World Health Organization. ICD-11 for Mortality and Morbidity Statistics, 6A02 Autism spectrum disorder, Version 2025-01. – Classification system. Release page: https://icd.who.int/browse/2025-01/mms/en
2. Höhne E, Kamp-Becker I. Diagnostik der Autismus-Spektrum-Störung bei Kindern und Erwachsenen. Psychiatrie + Neurologie 2024;(1). – Expert overview (in German)
3. Höhne E, Kamp-Becker I. Diagnostik der Autismus-Spektrum-Störung. Pädiatrie 2024;(4+5):27–32. – Expert overview (in German)
4. DGKJP, DGPPN et al. Autismus-Spektrum-Störungen im Kindes-, Jugend- und Erwachsenenalter. Teil 2: Therapie. S3-Leitlinie, AWMF-Reg.-Nr. 028-047, 2021. – Guideline (in German); expired on 23 March 2026 (see no. 5)
5. DGKJP. Aktuelle Leitlinien (Eintrag 028-047: „Gültig bis 23.03.2026“). https://www.dgkjp.de/wissen/aktuelle-leitlinien/ – Professional society (website in German)
6. Zeidan J, et al. Global prevalence of autism: A systematic review update. Autism Research 2022;15(5):778–790. https://doi.org/10.1002/aur.2696 – Systematic review
7. Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM). ICD-11 (Informationsseite zur Einführung in Deutschland). https://www.bfarm.de/DE/Kodiersysteme/Klassifikationen/ICD/ICD-11/_node.html – Authority (website in German)