BACKGROUND Irritable bowel syndrome (IBS) is a chronic disorder that has been found to be associated with psychiatric disorders and a history of physical and/or sexual abuse. To date, the relationship of posttraumatic stress disorder (PTSD) and IBS has not been investigated. The primary purpose of this study was to examine the relationship of IBS and PTSD. METHOD Fifty consecutive IBS patients admitted to a clinical treatment study were assessed for IBS, trauma history, and psychiatric disorders. RESULTS Twenty-seven IBS patients (54%) met criteria for a psychiatric diagnosis at some time in their lives. Twenty-two patients (44%) reported a trauma history. Eighteen (36%) were diagnosed with PTSD. Those IBS patients with a trauma history were more likely to have other comorbid psychiatric diagnoses. CONCLUSION These results suggest that IBS is often associated with psychiatric disorders, indicating that assessment and treatment of these comorbid conditions may be important in the treatment of IBS. PTSD, which had not been previously investigated in relation to IBS, had a high prevalence, indicating the need for careful trauma and PTSD assessment in patients with IBS. Patients with IBS who have a trauma history may be more at risk for other comorbid psychiatric disorders than IBS patients without a trauma history.