What is autism spectrum disorder? Autism spectrum disorder (ASD) is a lifelong developmental difference in how a person communicates, relates to others and experiences the world. Doctors diagnose it when a person has differences in two areas: social communication, and restricted or repetitive behaviors, interests and sensory responses. The CDC estimates that about 1 in 31 eight-year-olds in the United States has been identified with autism.
Quick answer
What is autism spectrum disorder: a developmental condition that affects social communication and includes repetitive behaviors, focused interests or sensory differences. Signs usually appear in the first two years of life, though it can be diagnosed at any age. “Spectrum” means every autistic person is different, with their own strengths and support needs.
Last checked: November 10, 2026. This is general information, not medical or legal advice.
What is autism spectrum disorder, in plain words?
Autism means a brain that develops and works differently, especially in communication, social connection and sensory experience. It is not an illness someone catches. The National Institute of Mental Health describes it as a neurological and developmental condition that affects how people interact, communicate, learn and behave.
The word “spectrum” matters. One autistic child may not use spoken words yet, while another talks at length about trains. One adult may need help with daily care; another works full time and needs quiet breaks. Since 2013, the American Psychiatric Association’s DSM-5 has used one diagnosis, autism spectrum disorder, instead of separate labels such as Asperger’s disorder.
The two core areas of autism
Every autism diagnosis rests on two areas. A clinician looks for lasting differences in both, starting in early childhood, that affect daily life. The CDC’s summary of the DSM-5 criteria lists what each area includes.
1. Social communication and interaction
All three of these must be present, now or in the past:
- Back-and-forth connection: sharing interests, feelings or conversation in the expected way.
- Nonverbal communication: eye contact, gestures, facial expressions and tone of voice.
- Relationships: making friends, adjusting to different social settings and pretend play.
2. Restricted and repetitive behaviors, including sensory differences
At least two of these four must be present:
- Repeated movements, speech or use of objects, such as hand flapping, lining up toys or repeating phrases (echolalia).
- A strong need for sameness and routines, with distress at small changes.
- Intense, focused interests.
- Over- or under-reaction to sound, light, touch, smell, taste or pain, or unusual sensory interest.
Some people learn to mask these traits, so they may only become clear when social demands grow, for example in middle school or at a new job.
Autism levels explained: what do levels 1, 2 and 3 mean?
The DSM-5 support levels describe how much support a person needs right now, rated separately for social communication and for repetitive behaviors. Level 1 means “requires support”, level 2 “requires substantial support” and level 3 “requires very substantial support”. A person can be level 1 in one area and level 2 in the other, and levels can change with age, skills and setting.
Levels describe support needs, not intelligence or a person’s worth. They replace older phrases like “high-functioning” and “low-functioning”, which many autistic people find misleading: a person who speaks fluently may still struggle with daily tasks.
| Level | What it describes | Examples of support |
|---|---|---|
| Level 1: requires support | Without support, social differences are noticeable; switching tasks, planning and handling change can be hard | Visual schedules, notice before changes, coaching for social situations or organization |
| Level 2: requires substantial support | Clear social communication differences even with support; repetitive behaviors are obvious to others and change is distressing | Planned daily support at home and school, communication tools, help through transitions |
| Level 3: requires very substantial support | Major communication differences and very limited social contact; change is extremely hard | Help across most of the day, including communication, daily care and safety |
Examples vary from person to person. In California, the level on a report does not decide services by itself. Regional centers use the Lanterman Act test of substantial limits in daily life, explained in our guide to regional center eligibility for autism. Schools use their own educational criteria.
Conditions that often come with autism
Many autistic people have other conditions too, and they can shape daily life as much as autism itself. The CDC lists these related characteristics and conditions:
- Delayed language skills or an intellectual disability (the diagnosis notes “with or without” each).
- Epilepsy or seizures.
- Gastrointestinal problems, such as constipation.
- Unusual eating and sleeping habits.
- Anxiety, stress or excessive worry.
Ask your doctor about each one separately. Pain, poor sleep or worry can show up as changes in behavior, so mention them. When therapies come up, ASC’s Options Policy on autism treatments explains why we describe options neutrally and don’t promote one approach.
Signs of autism and how it is diagnosed
There is no blood test or brain scan for autism. A trained clinician diagnoses it by watching the person, asking about their development and using standard tools. Signs often show by age 2, such as not responding to their name by 9 months or not pointing to share interest by 18 months.
- For toddlers, our early signs of autism in toddlers checklist lists what to watch for by age.
- For the steps, who can diagnose and what it costs, see how to get an autism diagnosis in California.
- Adults can be diagnosed too: NIMH notes autism can be diagnosed at any age.
Autism, neurodiversity and the words we use
Neurodiversity is the idea that brains naturally differ, and that autism is part of human variety, not something to erase. It does not deny real challenges. It means support should help the person thrive as themselves, not just look less autistic.
Language is personal: many autistic adults prefer identity-first words: “autistic person”. Many parents and professionals use person-first words: “person with autism”. Both are used respectfully on this site. The simplest rule is to ask the person, and to avoid “suffers from”, “normal kids” and functioning labels.
Newly diagnosed: what to do next in California
A diagnosis opens doors to help. In California, autism is one of the conditions named in the Lanterman Act, so regional centers may fund services after their own assessment. Children under 3 can get Early Start, and school districts assess for special education from age 3.
Our first 30 days after an autism diagnosis in California covers the order of calls and forms. For the full picture of diagnosis, regional centers and school services, read our guide to autism services in California.
Frequently asked questions
Does autism go away?
No. Autism is lifelong, but it is not static. Skills grow, support needs change, and many autistic people learn what helps them in different settings. Plans and supports should be reviewed as the person grows.
Is Asperger’s still a diagnosis?
Not in the DSM-5. In 2013, Asperger’s disorder, autistic disorder and PDD-NOS were combined into autism spectrum disorder. The CDC notes that people with a well-established earlier diagnosis should be given the autism spectrum disorder diagnosis. Some adults still describe themselves with the older word by choice.
How common is autism?
The CDC’s latest estimate, from 2022 data published in 2025, is about 1 in 31 children aged 8, and boys are identified more than 3 times as often as girls. For California numbers, see our page on autism rates in California.
Next step
For the clinical criteria in full, read the CDC’s page on autism testing and DSM-5 diagnosis and the National Institute of Mental Health’s overview of autism spectrum disorder.
Questions about a new diagnosis? Call the ASC information line at 1-800-869-7069, or find your local Autism Society affiliate for parent support near you. Below is this page as ASC first published it, with its original 2020 figures.
Original article (archived)
Archived page. Restored as the Autism Society of California last published it (archived November 2021). The figures date from 2020, and the wording reflects that time.
Autism is an umbrella term for a group of complex disorders of brain development, characterized, to varying degrees, by:
- Difficulties in social interaction
- Impairments in verbal and nonverbal communication
- Repetitive behaviors
- Intellectual and/or functional disability, poor attention
- Sometimes, difficulties in coordination, and health issues such as sleep and gastrointestinal disturbances
Autism has roots in very early abnormalities of brain development, but the most obvious signs of autism tend to emerge between 2 and 3 years of age.
Autism Rates have skyrocketed
National: The CDC identifies around 1 in 54 American children as on the autism spectrum, up from about 1 in 10,000 three decades ago.
California: California now counts more than 128,000 cases of severe, DDS-eligible autism in 2020, up from 3,262 just 25 years ago. This includes only those with severe functional limitations, if numbers of higher functioning but still disabled ASD individuals were included, the number would easily exceed 200,000.
Learn more
- Autism Society of America, autism-society.org