This study is working towards gaining a better understanding of the genetic and environmental factors involved in autism spectrum disorders (ASD), which includes autism, pervasive developmental disorder (PDD), and Asperger's syndrome. The investigators hope that information gained from this study will lead to new ways of diagnosing and treating ASDs.

Participation generally takes less than 2 hours to complete and travel to Children's Hospital Boston is not required. Participants are asked some questions about their medical and family history. The investigators also request permission to review medical records related to the autism spectrum disorders (ASD) diagnosis. Finally, the investigators obtain a small blood or saliva sample in order to search for genes that may be important in understanding ASD. The investigators can arrange for the blood draw through a participant's physician or a clinical laboratory and saliva samples can be obtained through the mail. The study questions are answered via telephone or mailed questionnaires. There is no cost to participate.

Inclusion Criteria:

• Clinical diagnosis of an Autism Spectrum Disorder (autism, pervasive developmental disorder (PDD), or Asperger's syndrome)
• Age > 18 months

Exclusion Criteria:

• Do not have the diagnosis of an ASD
• Participation in the "Phenotypic and Genetic Risk Factors in ASD" study at Boston Children's Hospital.

Children with a diagnosis of an Autism Spectrum Disorder (autism, pervasive developmental disorder (PDD), or Asperger's syndrome) and their parents and/or siblings