Irritable bowel syndrome (IBS), a functional gastrointestinal disorder, is present in 10% to 20% of the U.S. adult population. The syndrome is best defined as chronic abdominal discomfort with changes in stool frequency, consistency, and passage, with associated symptoms such as abdominal bloating or presence of mucus in stools. Several studies have shown that up to 70% to 90% of patients with IBS who seek treatment have psychiatric comorbidity, most notably mood and anxiety disorders. Recent studies have shown a high prevalence of IBS in psychiatric patients who seek treatment, with a prevalence of 19% in schizophrenia, 29% in major depression, and 46% in panic disorder among other disorders. Our article reviews the comorbidity of IBS in psychiatric patients and discusses implications for treatment.