The purpose of this literature review was to provide an overview of the research on gastrointestinal (GI) symptoms in autism spectrum disorder. Topics explored include the prevalence of GI symptoms, the importance of studying GI symptoms, the difficulties in diagnosis, as well as the questionnaire measures used to assess gastrointestinal symptoms. Research on the relationships between gastrointestinal symptoms and developmental regression, language and communication, autism severity, challenging behavior, comorbid psychopathology, sleep problems, and sensory issues is also discussed. The use of special diets is discussed also. Finally, recommendations for treatment are given as well as areas where future research is needed.