How to treat patients with irritable bowel syndrome (IBS) who do not respond to pharmacotherapy is an unsolved problem. Psychotherapy, which has been reported on in previous studies, is available only in specific centers. We describe in this study a novel and simple psychotherapy; that is, the fasting therapy (FT) for treatment of patients with IBS. Of 84 inpatients with IBS, 58 patients who still had moderate to severe IBS symptoms after 4-week basic treatment were investigated retrospectively. Of the 58 patients enrolled in this study, 36 underwent FT, whereas the remaining 22 received a consecutive basic treatment (control therapy). There were no significant differences in the 4-point severity scales of gastrointestinal and psychological symptoms between the 2 groups before the start of FT. The basic treatment consisted of pharmacotherapy and brief psychotherapy, whereas the FT consisted of 10 days of starvation followed by 5 days of refeeding. Changes in scores of symptoms before and after each treatment were analyzed. FT significantly improved 7 out of the 10 symptoms assessed; that is, abdominal pain-discomfort (p < .001), abdominal distension (p < .001), diarrhea (p < .001), anorexia (p = .02), nausea (p < .01), anxiety (p < .001), and interference with life in general (p < .001). However, the control therapy significantly improved only 3 out of the 10 symptoms assessed; that is, abdominal pain-discomfort (p = .03), abdominal distension (p < .01), and interference with life (p = .01). Our results suggest that FT may have beneficial effects on intractable patients with IBS.