&NA;Patients with a personal history of rectal cancer are considered at high risk for metachronous large‐bowel primaries. Since a malignant growth was the main reason for performing a colostomy in patients followed at the centers of the authors' association (AISTOM), a correct follow‐up approach for these patients is very important. A multicentric clinical trial was thus carried out to evaluate the efficacy of transstomal endoscopic exploration (TEE) of the residual colon, and data collection began on May 31, 1984. Nine hundred fifty‐seven patients were submitted to TEE after curative abdominoperineal resection (Miles) for rectal cancer. The male‐female ratio was 1.3;89.6 percent of the patients were over 50 years of age. A family history of large‐bowel cancer was present in 18 percent, and in 23 percent of the patients the cancer was associated with synchronous adenomas. Only 31 percent of the patients had colonoscopy or double‐contrast barium enema x‐ray beyond the neoplastic area before the surgery. TEE was done in 96.8 percent of the patients; in 3.3 percent the examination was not possible, mainly for stenosis of the stoma (in 2.3 percent). In 82 percent of the patients a complete large‐bowel exploration was possible: a new large, bowel cancer was found in 22 patients (2.2 percent) and an adenoma in 183 patients (19.1 percent). These results show that, because it is safe, practical, and effective, endoscopy plays an important role in the follow‐up of ostomates.