The irritable bowel syndrome is a highly prevalent condition whose underlying aetiology is not understood. While many patients respond to a combination of gastrointestinal antispasmodics, bulking agents and dietary manipulation, controlled clinical trials have suggested that the benefit is only marginal and is due mainly to the large placebo effect found in this condition, which has been calculated to range between 54 and 81%. Associations between the syndrome and psychological and social stresses suggest, however, that treatment involving a systematic approach to the management of symptoms may hold out real therapeutic possibilities. In the current study, 42 IBS patients were randomly allocated to either medical treatment or to behavioural psychotherapy with a nurse therapist. They were assessed initially and at 4 and 9 months. There was a general improvement over the 9 months on a number of physical and psychological symptoms measured. However, no differences were found between treatment groups except for changes in two avoidance scores. A significant correlation was found, however, between improvement in the bowel symptoms of IBS (stomach pain and diarrhoea) and improvement in the psychological symptoms measured by the Clinical Interview Schedule, suggesting a close interrelationship between the two.