Background: * Autism spectrum disorders (ASDs) are a group of developmental disorders that affect communication, social interaction, and behavior. Relatively little is known about the relationship between genetics and behavior among these individuals and their close relatives. Researchers are interested in using interviews and rating scales to better understand these issues, as well as collecting brain scan data and genetic samples for testing and comparison. * By comparing test results and genetic samples from healthy volunteers, people with ASD, and parents (or caregivers or legal guardians) of the first two groups, researchers hope to better understand the neuroscience of ASD.

Objectives: * To learn more about the brain in healthy people and in people with autism spectrum disorders. * To study genes that might be involved in autism spectrum disorders by collecting DNA samples from participants.

Eligibility: The following groups of participants will be eligible for the study: * Individuals between 5 and 89 years of age who have autism spectrum disorders. * Healthy volunteers between 5 and 89 years of age. * Cognitively impaired children between 5 and 17 years of age. * Parents/caregivers/legal guardians of individuals in the above three groups.

Design: * Participants will visit the National Institutes of Health Clinical Center for research tests, which will be administered over multiple visits. Researchers will determine the specific tests to be administered based on the medical history of the study participant. * Researchers will study the brain through interviews, tests of thinking and memory (neuropsychological tests), brain imaging with magnetic resonance imaging (MRI), and magnetoencephalography (MEG). * The study will also collect blood or saliva to obtain a DNA sample.