Surveillance after colorectal carcinoma and adenoma includes colonoscopy, which is a demanding procedure for the patient, doctor, and society. Therefore, it was investigated whether a simple fecal occult blood test could replace colonoscopy. Hemoccult-II (H-II) was performed before 1,244 colonoscopies in patients with previous cancer and before 328 colonoscopies in an adenoma surveillance program. The H-II test was positive in 3 of 9 patients with local recurrence, in 2 of 13 with metachronous cancer, and in 31 of 186 with adenomas. The test was positive more often in patients with large and multiple adenomas, sigmoid adenomas, and adenomas with villous elements and moderate-to-severe dysplasia, but the sensitivity did not reach more than 25 to 40 percent. It was concluded that markers more sensitive than H-II are needed to detect metachronous cancers and new adenomas. In the meantime, colonoscopy has to be used with intervals of several years, but not for detection of local recurrent cancer, which in most cases may be found by simpler means.