A prospective study was undertaken to establish the role of individualized diet counselling in the management of 137 outpatients with Crohn's disease. Individualized dietary counselling for 6 months was associated with a significant decrease in the Crohn's disease activity index, an increased incidence of disease remission, a decreased need for prednisone and Salazopyrin therapy, a reduction in the number of days spent in hospital, and a reduction in the amount of time lost from work due to Crohn's disease, when compared with control patients who did not receive dietary counselling but who were seen regularly in follow-up under similar circumstances. Improvement with diet counselling was more likely to occur in patients who had not previously been subjected to small bowel resection, and occurred in patients with active or inactive disease. The effect of counselling 58 patients was assessed over a further 6 months (for a total 12-month period); there was a persistently reduced Crohn's disease activity index and a continued decreased number of lost days of work. The mechanism for these beneficial effects of diet counselling was not established. It is suggested that individualized diet counselling, aimed at optimizing the patient's nutritional status, may play a role in the management of patients with Crohn's disease.