During the past 20 years there has been growing interest in the importance of nutritional factors in the pathogenesis of inflammatory bowel disease. There are so far no definite links between ulcerative colitis and diet, but links with Crohn's disease have been studied by both epidemiologists and clinicians. Epidemiological studies, although retrospective, have suggested that patients with Crohn's disease eat more sugar and sweets that control individuals; however, when dietary sugar is restricted, there is little clinical benefit. The clinical approach to nutrition in Crohn's disease has been by the use of elemental diets, which will produce symptomatic and objective remission in up to 90% of compliant patients. Those who return to normal eating soon relapse but, in some studies, have enjoyed prolonged remission on exclusion diets. The foods excluded have been not sugar, but predominantly cereals, dairy products and yeast. Attention has now switched to the possible harmful role of fat in Crohn's disease. The efficacy of elemental feeds appears to depend not on the presentation of nitrogen but on the amount of long chain triglyceride present. Increases in recent years in the frequency of Crohn's disease in Japan have been correlated with increased dietary fat intake, and a recent study suggested that W-3 fatty acids, which are metabolized by immunomodulatory leukotrienes and prostaglandins, may have a beneficial role to play. The links between nutrition and Crohn's disease have now become strong and the role of fat may be the most exciting of all.