Irritable bowel syndrome is a disease that can be diagnosed positively on the basis of an established series of criteria and limited exclusion of organic disease. It is the most common disease diagnosed by gastroenterologists and affects about 20% of all people at any one time. Symptoms fluctuate, and the overall prevalence rate is relatively constant in Western communities. Ten per cent of patients present to their physicians; the illness has a large economic impact on health-care utilization and absenteeism. Irritable bowel syndrome is a biopsychosocial disorder in which three major mechanisms interact: psychosocial factors; altered motility; and/or sensory function of the intestine. Management of patients is based on positive diagnosis of the symptom complex, limited exclusion of underlying organic disease and institution of a therapeutic trial. If patient symptoms are intractable, further investigations are needed to exclude significant motility or other disorders. Symptomatic treatment includes fibre for constipation, loperamide for diarrhoea and low-dose antidepressants or infrequent use of antispasmodics for pain; novel pharmacological agents, psychotherapy and hypnotherapy are being evaluated.