Over a 3-year period, all patients referred for barium enema examination had a double-contrast barium enema and flexible sigmoidoscopy performed on the same day. A total of 462 joint examinations were performed. Abnormalities were found in 193 patients by the use of barium enema, 164 patients by using sigmoidoscopy and 294 by the use of both methods of investigation. Sigmoidoscopy was superior to barium enema in the detection of polyps and inflammatory bowel disease but barium enema was more sensitive for diverticular disease. The presenting symptoms had no predictive value in distinguishing carcinoma, polyps and diverticular disease. Diverticular disease did not reduce the sensitivity of barium enema examination to polyps in the sigmoid colon. Fibreoptic sigmoidoscopy immediately before barium enema was well tolerated by patients. The investigations were complementary in the diagnosis of colonic polyps, inflammatory bowel disease and diverticular disease.