We studied 114 patients affected by irritable bowel syndrome (IBS) (group A = 53 patients, group B = 61). Group A received diet with high content of roughage (20 g of fibers) and 10 g of bran, group B received otilonium bromide (OB) 40mg tid and normal diet (10-15 g of fibers). Abdominal pain, abdominal distension, bowel movements were evaluated before treatment (T0) at the end (T24) and after 12 months (T12). In group B otilonium bromide induced a significant improvement (p less than 0.01) of abdominal pain and distension when comparing T0 with T24. In group A diet produced an improvement, albeit not significant, of the aforementioned parameters at T24. On the basis of our data OB seems to be more effective than a high-fiber diet in the treatment of IBS.