An analysis was made of the prognosis over a one-year follow-up period of a consecutive series of 86 out patients with irritable bowel syndrome (SII) who were treated randomly with an antispasmodic (otilonium) or a tranquilizer (clobazam), and the existence of factors, mainly psychological, that could worsen it was determined with the Zung anxiety test and the Hamilton depression scale. We confirmed that irritable intestine syndrome is a chronic disease, with a mean course of 13 +/- 12.5 years at the time of consultation. A large proportion of patients had permanent problems (58.1%) and did not experience important changes in the intensity of symptoms throughout evolution (68.6%). Although most improved initially with the treatment instated (76.7%), the improvement was rarely complete (11.8%). A year after beginning treatment, 61.6% were the same or worse than before the index consultation. In the group of patients with a good course, the proportion of those that correctly followed medical treatment and of those who had experienced more or less lengthy asymptomatic periods before consultation was significantly larger. In the group of patients with poor evolution, the scores on the Zung anxiety test and Hamilton depression scale were significantly higher than in those who evolved favorably. Neither consultation of a specialist nor the treatment used in this study seem to have contributed to an evident improvement in the prognosis.