Autistic disorder is a complex neurodevelopmental disorder that affects a person's ability to communicate, respond to their surroundings or form relationships. Dr. Leo Kanner, a psychiatrist at Johns Hopkins University, first described autism in 1943. Autism is typically diagnosed in children between the ages of two and three years. Autism affects individuals of all racial, ethnic and socioeconomic backgrounds. Males are three times more likely to be affected than females.

Autistic disorder is a pervasive developmental disorder (PDD). Individuals with a PDD have symptoms that affect communication, socialization and behavior. There are five diagnoses that fall under the category of PDDs. These are:

• autistic disorder,
• Asperger disorder,
• Rett syndrome,
• child disintegrative disorder, and
• pervasive developmental disorder—not otherwise specified (PDD-NOS).

The distinctions between these diagnoses are made based on subtle differences in severity, age of onset of symptoms and degree of language development. There is no test that can diagnose a PDD. Diagnosis is made based on clinical evaluation, including interviews, observation and psychological measurements. An individual may be given a diagnosis of more than one PDD. This may be due to changes in their symptoms over time or to variability in the methods of clinical assessment.

The specific causes of autism are not yet known. There is significant evidence that there is a strong genetic component. Environmental factors may also play a role in the development of autism. It is likely that there is no one specific cause for autism, but rather that it results from a complex interaction of genetic and environmental factors.

At this time, there is no cure for autism. There are interventions that may lead to improved development of language and social skills and decreased behavioral problems. There are both educational/behavioral interventions (including applied behavioral analysis) and pharmacologic interventions (medications such as Ritalin). Medications are usually taken to address a specific behavior, such as aggression, tantrums or hyperactivity.