Autism develops in childhood, but sometimes it isn’t diagnosed until adulthood. While some symptoms can present in infants, they generally become apparent in toddlerhood.

Children can be reliably diagnosed with autism around 2 years old.

Autism Diagnosis: When Do Symptoms Appear? 

Since autism is a spectrum disorder, there is a range of symptoms that can appear and shift over the course of a person’s life.

Symptoms may also depend on the severity of autism. Some people with autism do not need a high level of medical care, but they may struggle with social or communication issues, for example.

Typically, pediatricians flag younger children for a potential autism diagnosis at a routine visit. Doctors will screen for developmental disorders, including autism, at various stages of development. As a parent, you may notice some autism symptoms in your child and report these to your doctor.

A developmental pediatrician, child psychologist, or pediatric neurologist gives an official diagnosis.

The Centers for Disease Control and Prevention (CDC) report that autism symptoms are most apparent in children starting around 2 years old. However, screening for developmental disorders begins earlier than that.

As the medical understanding of autism has been refined over the past few decades, more adults are diagnosed with autism

Diagnosing Autism in Children

Your child will undergo both developmental monitoring and developmental screening by their pediatrician. Developmental monitoring involves watching how your child grows and changes over time, measuring them against what is considered standard physical, mental, emotional, and social development for their age group.

While not all children meet the specific milestones listed, that does not inherently mean that something is wrong; however, failing to meet some can indicate a developmental disorder like autism.

Developmental screening is a closer look at your child’s development, usually involving a brief test or questionnaire you will answer. The American Academy of Pediatrics (AAP) recommends developmental screenings at the following ages: 

  • 9 months old
  • 18 months old (1.5 years)
  • 30 months old (2.5 years)

These screenings will look for any developmental disorders, but AAP recommends autism-specific screenings at the following ages:

  • 18 months (1.5 years old)
  • 24 months (2 years old)

Additional screenings are recommended as needed based on risk factors. You may notice that your child makes fewer sounds, does not acquire words, stops making eye contact, or is not interested in socializing with you or others as early as 6 months old. Still, a doctor is not likely to make an official diagnosis until after 2 years old.
There are different levels of autism severity. For people with moderate or severe autism, symptoms may be noticeable earlier, or they may be clearer to a doctor because they meet the definition of autism. These symptoms include struggling to make eye contact, learning very few words, not learning to speak until later, preferring to play alone and refusing to socialize, struggling with emotional regulation, refusing a wide range of foods, and struggling with sensory stimulation problems.

In other cases, symptoms may be mild. You may assume your child is shy, introverted, or even slightly physically awkward. These symptoms may be easy to mask, but they can indicate autism. 

Diagnosing Autism in Adults

Today, 1 in 44 children is diagnosed with autism. This is a higher rate than 20 years ago because the approach to recognizing this condition is continually being refined so it is more accurate. This also means that more adults are being diagnosed with autism.

Most often, adults who have undiagnosed autism are considered more introverted. They are much less likely to socialize, and they are more likely to become stressed in social environments. They are more likely to stick to a routine and carry out repetitive actions. They may struggle to understand others’ points of view because they have a harder time understanding others’ emotions or inner worlds.

Social interaction and communication are challenging, even though many other aspects of their lives are manageable. Adults with autism are often quite successful, with the exception of feeling “awkward” or “out of place.”

Adults with autism are most likely to be diagnosed by a behavioral therapist who discusses aspects of their childhood, including delays in speech, behavioral struggles, and learning difficulties. Signs of autism in adults may include the following: 

  • Physical awkwardness or clumsiness
  • Trouble starting or maintaining conversations
  • Few close friends
  • Struggling to make eye contact
  • Difficulty regulating emotions, especially when under stress 
  • Trouble understanding change
  • Hyperfocus on one or two topics
  • Sensitivity to sensory input like smells, tastes, textures, or sounds that do not seem to bother others
  • Interest in few activities and preference for solitary activities
  • Trouble reading others’ emotions, including body language and facial expressions
  • Social anxiety 
  • Repetitive behaviors and organizing things in a specific way
  • Stimming 

Symptoms can also differ between men and women. For example, women with autism may cope better with social situations, but they may be much quieter and more reserved.

Adults with autism are more likely to have depression and anxiety compared to their neurotypical peers. This may be because they have spent much of their lives feeling ostracized, not fitting in, and wondering why they are not like their friends.

Increasingly, adults with autism self-diagnose and then seek help from a therapist or specialist. This is because milder autism symptoms that escape notice in children can be masked through adolescence and young adulthood.

To help adults who think they may be on the autism spectrum, specialists developed the Adult Repetitive Behavior Questionnaire (RBQ-2), which measures the extent to which adults are impacted by repetitive and restrictive behaviors that appear in moments of stress. If you take this test yourself, you may use it to begin a conversation with a behavioral therapist to get the correct diagnosis. 

Get the Help You Need

Since autism is a developmental disorder, symptoms will be present throughout a person’s life, even if they are not appropriately diagnosed until adulthood. Autism does not have “late onset,” and symptoms will not go away.

With good behavioral therapy with an applied behavior analyst (ABA), children with autism can improve behavior by learning new skills to manage their emotional regulation, communication skills, and more. Children diagnosed with autism may need physical therapy, occupational therapy, nutritional support, and other forms of therapy alongside ABA therapy, but these are all geared to helping the child become as independent and happy as possible.

Autism can be diagnosed at any point in a person’s life. Moderate and severe symptoms are more likely to be diagnosed in children, while milder symptoms may escape diagnosis for several years, even into adulthood. Children benefit the most from consistent ABA therapy and other support therapies as needed, but adults can benefit from these measures as well.

In adulthood, getting a diagnosis of autism often comes with a sense of relief. This diagnosis can correct previous misdiagnoses of severe depression, social anxiety, obsessive-compulsive disorder (OCD), and even schizophrenia. You can then start getting appropriate behavioral therapy to help you improve your overall quality of life. 


Screening and Diagnosis of Autism Spectrum Disorder. (March 2020). Centers for Disease Control and Prevention (CDC). 

Data & Specifics on Autism Spectrum Disorder. (September 2020). Centers for Disease Control and Prevention (CDC).

CDC’s Developmental Milestones. (June 2020). Centers for Disease Control and Prevention (CDC).

When Do Children Actually Show Symptoms of Autism? (January 2017). Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHHD).

Signs of Autism in Adults. (April 2019). NHS.

Researchers Develop First Autism Symptom Self-Assessment for Adults. Autism Speaks.