Autism spectrum disorder, or ASD, includes what used to be called Autistic Disorder, Asperger syndrome, or Pervasive Developmental Disorder – Not Otherwise Specified, all of which affect a person’s social and emotional skills and nonverbal communication. ASD has many similarities to ADHD, but there are also differences between the two.

Can a person be diagnosed with both ADHD and ASD?

More than half of all individuals who have been diagnosed with ASD also have signs of ADHD. In fact, ADHD is the most common coexisting condition in children with ASD. On the flip side, up to a quarter of children with ADHD have low-level signs of ASD, which might include having difficulty with social skills or being very sensitive to clothing textures, for example.

Why do ADHD and ASD coexist so often and what are the similarities between them?

Both ADHD and ASD are neurodevelopmental disorders (brain development has been affected in some way). That means both conditions/disorders affect the central nervous system, which is responsible for movement, language, memory, and social and focusing skills. A number of scientific studies have shown that the two conditions often coexist, but researchers have not yet figured out why they do.

With ADHD or ASD, brain development has been affected in some way. Most importantly, that includes the brain’s executive functioning, which is responsible for decision making, impulse control, time management, focus, and organization skills. For many children, social skills are also affected. Both ADHD and ASD are more common in boys.

Although adults can have both ADHD and ASD, the combination is not as common as it is in children. While ASD is considered a lifelong disorder, long-term studies have shown that in one-third to two-thirds of children with ADHD, symptoms last into adulthood.

What are the differences between ADHD and ASD?

Many children are first diagnosed with ADHD around the time they start preschool or kindergarten because their behavior contrasts with that of their classmates. ADHD can cause children to be restless all the time, act impulsively, and have a hard time paying attention. But some children with ADHD have different signs—focusing all their attention on one toy, for instance, and not wanting to play with anything else.

For some children with ASD, the signs are noticeable before they reach their second birthday. For others, signs of ASD may not be clear until they are school-aged and their social behaviors are clearly different from their classmates’. Children with ASD often avoid eye contact and don’t seem interested in playing or engaging with others. Their ability to speak may develop slowly or not at all. They may be preoccupied with sameness in textures of food or in making repetitive movements, especially with their hands and fingers.