To establish the short-term and long-term results of current treatment of irritable bowel syndrome (IBS), 104 patients were studied prospectively. All patients were treated similarly and the results were assessed after a few weeks and then after at least 5 years. IBS can be diagnosed more easily than has been suggested--72% of this series were correctly diagnosed by their referring doctor, and only 12% required radiological studies to exclude organic disease. The response to treatment was considerably better than expected, possibly because of the more aggressive use of high-fibre diets and bulking agents. Thus, 85% of patients were rendered virtually symptom-free in the short term, and 68% were still virtually symptom-free 5 years later. The response to treatment was better in men than in women, in those with constipation than with diarrhoea, when the symptoms had initially been triggered by an episode of acute diarrhoea, and in patients with a relatively short history. With a few simple investigations, sympathetic explanation, and appropriate treatment, most patients with IBS have a good prognosis.