The purpose of this research study is to help us learn if children with Autism Spectrum Disorder (ASD) have gastrointestinal (stomach and intestine) problems more frequently than children without ASD do. The investigators hope to learn if children with ASD and gastrointestinal (GI) disorders have certain Problem Behaviors (PB), such as self-injury and aggression, more than children with ASD but no GI disorders do. The investigators want to learn if the Gastrointestinal Symptoms Questionnaire (GIQ) can help us tell which children with ASD also have gastrointestinal disorders.

Hypothesis 1: Children with ASD exhibit high rates of symptomatic GI dysfunction that are not identified by current diagnostic evaluation.

Hypothesis 2: Painful or discomfort-causing gastrointestinal dysfunctions contribute to an elevated incidence or severity of PB in an identifiable subpopulation of PB-expressing children. The investigators anticipate that the proposed study will raise the standard of medical care for children with ASD by improving current methods of identifying GI dysfunction and determining whether there is a significant relationship between GI dysfunction and PB in this population.

Inclusion Criteria:

• Children who are ATN Registry subjects between 2 and 17 years old (inclusive)
• Meet criteria for an ASD according to the diagnostic measures Autism Diagnostic Observation Schedule (ADOS) and DSM-IV Symptom Checklist, which were conducted at an established ATN center within the last 18 months

Exclusion Criteria:

• Diagnoses of Rett Syndrome, Childhood Disintegrative Disorder, or other genetic disorders (e.g. Fragile X, Down syndrome, etc.).

131 nonselected subjects with ASD