The purpose of this study was to estimate the prevalence of chronic 
gastrointestinal symptoms in a general population of children with autism or 
autistic spectrum disorder (ASD). The study site was a clinic specializing in 
ASD in a large pediatric medical center serving a 10 county area in the 
midwestern USA. In a sample of 137 children, age 24-96 months, classified as 
having autism or ASD by the Autism Diagnostic Observation Schedule-Generic, 24 
percent had a history of at least one chronic gastrointestinal symptom. The most 
common symptom was diarrhea, which occurred in 17 percent. There was no 
association between chronic gastrointestinal symptoms and a history of 
developmental regression. The potential phenotypic association between autism 
and gastrointestinal symptoms is discussed.