Background: Gastrointestinal (GI) symptoms are frequently reported in children with Autism SpectrumDisorder (ASD), and an impact of GI comorbidity on ASD behavioral problems has been hypothesized.Aims: To explore the type and the prevalence of GI symptoms in ASD patients and typical development(TD) controls, and to investigate their possible association with behavioral problems.Methods: A total of 230 preschoolers were included in this study. Specifically, four groups of children wereevaluated: ASD individuals suffering from GI symptoms (ASD/GI+), ASD subjects without GI symptoms(ASD/GI−), TD peers with (TD/GI+) and without (TD/GI−) GI symptoms. Parental report of behavioralproblems and GI symptoms were assessed through the Child Behavior Check List 1½–5.Results: A significant higher percentage of ASD (37.4%) versus TD (14.8%) with GI symptoms was observed.‘Constipated’ and ‘Not-Eat’ were the most frequent GI symptoms both in ASD and in TD groups, butthey were evaluated as more severe in ASD patients. ASD/GI+ children had more anxiety problems,somatic complaints, externalizing and total problems than ASD/GI− individuals. TD/GI+ did not showmore behavioral problems than TD/GI−.Conclusion: Development of evidence-based guidelines for identification of GI problems in ASD preschool-ers is warranted. GI symptomatology should be accurately assessed, especially in ASD children withanxiety and/or externalizing behavioral problems.