The aetiology of inflammatory bowel disease (IBD) remains unknown, and many methods of treatment have been advocated. Patients with IBD are often nutritionally deficient and in negative nitrogen balance. The cause is multifactorial and includes decreased intake and absorption due to previous resection or mucosal involvement or increased exudation. General recommendations of vitamin and mineral supplements are usually made for these patients. Diet may have a more fundamental role in the aetiology and treatment of Crohn's disease, although this is not certain. Several controlled studies have confirmed that an elemental diet is as effective as steroids in inducing a remission in patients with acute Crohn's disease. Bacteria have also been implicated in the aetiology of Crohn's disease. Dietary measures may alter the intestinal flora and could result in a decrease of toxin production, which has been shown to correlate with clinical improvement. Although elemental diets are not effective in the treatment of ulcerative colitis, dietary measures may still be important. Preliminary studies suggest that eicosapentaenoic acid, which inhibits the production of mediators of inflammation by competing with enzymes in the arachidonic acid pathway, may be effective. Recent findings of increased faecal bile acids in patients with long-standing ulcerative colitis who developed dysplasia or carcinoma suggest that dietary measures may counteract these developments. It does appear that nutritional therapy in patients with IBD has both a primary and adjunctive role.