The sensitivity between double contrast barium enema (DCBE) and sigmoideoscopy in diagnosing neoplastic lesions in the sigmoid colon was compared in patients with diverticulosis. In 52 patients with severe diverticulosis (> or = 15 diverticulas) the DCBE detected one out of 4 polyps found by sigmoideoscopy. In the remaining 54 patients with mild diverticulosis (< 15 diverticulas) DCBE detected 7 out of 10 polyps found by sigmoideoscopy. Successful bowel preparation did not influence the outcome of the DCBE. Sigmoideoscopy was incomplete in 17 (16%) of the patients; females were more difficult to examine than males (p = 0.012), as were those with a previous pelvic operation (p = 0.032). We conclude that neither DCBE nor sigmoideoscopy alone is sufficient to detect all neoplastic lesions in the sigmoid colon in patients with sigmoid diverticulosis of the colon.