Signs and Symptoms of Autism

The signs and symptoms of autism are usually seen before age 3. They include impairments in communication, social interactions, and responsiveness, as well as possible obsessive or repetitive behaviors.

It's said that "if you've met one person with autism, you've met one person with autism." That's because the appearance of autism can vary from person to person in the types of symptoms and their severity. One person with autism may be very verbal, bright, and engaged, while another is non-verbal, intellectually challenged, and almost entirely self-absorbed.

girl lining up crayons
 Kinzie Riehm / Getty Images

Frequent Symptoms

The National Institutes of Mental Health has created a list of symptoms that are often seen in autism. It's important to bear in mind that none of these symptoms on their own is likely to indicate autism. Autism is a pervasive developmental disorder, which means that a child must have many of these symptoms in order to qualify for a diagnosis.

By the same token, however, many children reach early milestones on time (or even early) and still qualify for an autism spectrum diagnosis. While some children may seem to develop typically for a while and then develop symptoms, others may have obvious symptoms from infancy.

Early signs and symptoms of autism include:

Symptoms of autism are often present before the age of 3. Some children, however, have mild symptoms that may not be obvious at a very young age and such children may, as a result, be diagnosed after age 3.

When that happens, it's usually because they have several later indicators, such as:

If symptoms such as these suddenly appear in a child older than 3, and those symptoms were definitely not present from an earlier age, the child would not qualify for an autism diagnosis. The child would, however, almost certainly receive a different developmental or psychiatric diagnosis.

Rare Symptoms

People with autism are more likely to experience:

  • Seizures
  • Intellectual disability
  • Savant syndrome (extraordinary abilities in one very specific area, such as mathematics)
  • Hyperlexia (early ability to decode words without understanding them)
  • Synesthesia (association of words or ideas with sounds, colors, tastes, etc.)
  • Low muscle tone and/or difficulties with fine and gross motor skills

Complications/Sub-Group Indications

Autism has many proposed sub-groups, which often align with the presence of other conditions.

Symptoms in Boys vs. Girls

The vast majority of people diagnosed with autism are boys and men. This may be, in part, because autism tends to look very different in girls and women and, as a result, it may not be recognized as often.

In general, boys with autism show overt symptoms such as stimming (pacing, flicking fingers, rocking). They may be quite loud, get upset easily, or become angry when required to take part in activities that are outside their comfort zone. These behaviors naturally draw the attention of parents, teachers, and doctors.

Girls and women with autism, on the other hand, tend to be very quiet and withdrawn. They are often loners who choose not to participate in group activities. Because many accept the cultural notion that girls are often quiet and unengaged, these behaviors are much easier to mistake for shyness or normal social reticence.

Of course, there can be wide variations depending on the individual.

Association With Other Conditions

Most of the symptoms of autism are also symptoms of other developmental and mental health disorders. As a result, it is not unusual for children with autism to have multiple diagnoses.

In addition, people with autism seem to be more prone to other problems not listed in the diagnostic criteria.These problems include sleep disorders, gastrointestinal disorders, self-abusive behavior, and more.

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) includes specifiers for these co-existing conditions:

  • Intellectual impairment
  • Language impairment
  • Attention deficit hyperactivity disorder (ADHD)
  • Developmental coordination disorder
  • Disruptive behavior disorder
  • Impulse control disorder
  • Conduct disorder
  • Depressive disorder
  • Bipolar disorder
  • Tics
  • Tourette's disorder
  • Self-injury
  • Feeding disorder
  • Elimination disorder
  • Sleep disorder
  • Catatonia

When to See a Doctor

It can be very tough for a parent to determine whether behaviors are symptoms of autism or just ordinary variations in development. How much lining up of toys is excessive? How much desire for repetition is normal?

There is also the possibility that some developmental differences are caused by non-autism-related issues. For example, not responding to a name could very well be a symptom of hearing impairment. Late talking could be due to aphasia or apraxia of speech.

To properly diagnose autism, professionals use a set of specific tests that actually measure a child's symptoms. They may also decide that your child should undergo testing for hearing impairment or speech issues that are unrelated to autism.

For that reason, if you're concerned about your child, take your concerns to your pediatrician. If the pediatrician is not able to help, and you still have worries, it may be time to make an appointment with a developmental pediatrician or another diagnostician.

Frequently Asked Questions

  • At what age do clear signs and symptoms of autism develop?

    Signs of autism usually develop before a child reaches 3 years of age. These signs include impaired communication, social skills, or responsiveness, as well as repetitive behavior. However, sometimes children with high-functioning autism aren’t diagnosed until later. Since autism presents differently in girls, they may also be diagnosed at a later age.

  • What are signs of autism at 9 to 12 months old?

    Infants with autism may exhibit a delay in babbling or pointing (which usually develop in the first year of life), as well as impairments in language development—not saying single words by 16 months of age. Among other symptoms, they may also be under-responsive to social stimuli or not respond to hearing their name.

  • What are signs of high-functioning autism?

    High-functioning autism, once known as Asperger’s syndrome, combines normal or unusual intelligence with symptoms of autism. A child may do exceptionally well academically, for example, but have trouble relating to peers in social settings. Other signs of high-functioning autism include a susceptibility to sensory overload; anxiety or depression; lack of organizational skills and problems with “executive function”; emotional dysregulation; and struggling with verbal communication.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  9. National Institute on Deafness and Other Communication Disorders. Autism Spectrum Disorder: Communication Problems in Children.

Additional Reading

By Lisa Jo Rudy
Lisa Jo Rudy, MDiv, is a writer, advocate, author, and consultant specializing in the field of autism.