The cause of autism is not yet known. Although it is generally accepted that autism involves differences in the development and function of the brain. Researchers are currently investigating theories that look at the connection between autism, genetics, and medical problems such as viral infections. Others are investigating the relationship between environmental causes of autism, such as exposure to chemicals, allergens or vaccines. To date, researchers have not conclusively proven a link between any of these areas and autism.

Contrary to some earlier theories, it is now known that autism is not caused by poor parenting, nor is autism a mental illness. No known psychological factors have been shown to cause autism in children.