Irritable bowel syndrome (IBS) is a functional disease with good prognosis, which is diagnosed by exclusion of possible causative organic diseases. However, since the patients tend to have strong psychotic symptoms including anxiety, tension, depression, irritation and insomnia, this syndrome has to be elucidated as a psychosomatic disease. Although the symptoms are usually limited to gastrointestinal symptoms such as abdominal pain and abnormal bowel movements, many patients also manifest some kinds of psychiatric abnormalities such as hypochondria, depression, hysteria, panic disorder and posttraumatic stress disorder. Especially, the prevalence of depression is high. Therefore, use of psychotropic drugs is efficient in treating IBS. Antidepressant agents including tricyclic agents such as amitriptyline, trimipramine, imipramine, clomipramine, amoxapine and nortriptyline; tetracyclic antidepressant; antidepressants such as SSRI and SNRI; sulpiride; benzodiazepine class anxiolytic agents; tandospirone; and Chinese herbal medicine are being used. IBS is a stress-related disease. Therefore, in spite of the importance of pharmacotherapy, patients should also be instructed to avoid the stress that aggravates the symptoms in all aspects of daily life.