Patients with irritable bowel syndrome (IBS) have chronic abdominal symptoms and their health perceptions are impaired though the causes of their symptoms are not explained by routine examinations. IBS patients often show psychological symptoms represented by anxiety and depression, and many of them have the complication of anxiety disorder including panic disorder, depressive disorder, PTSD and so on. In our experience, 27% of IBS patients have the co-morbidity of panic disorder, and these two disorders exacerbated symptoms each other. Such condition impairs health-related quality of life in IBS patients. Psychological and behavioral therapy may benefit in symptomatic relief in IBS patients, suggesting strong participation of phsycological aspects in IBS patients.