PURPOSE:Colonoscopic surveillance is recommended for patients with adenomatous polyps. Significant cost savings would result from identification of subgroups of patients in whom less costly surveillance would suffice. This study was performed to determine the natural history of patients undergoing removal of isolated rectosigmoid adenomas and to establish whether flexible sigmoidoscopy might be adequate for follow‐up.METHODS:A retrospective review of a database of 7,677 colonoscopies, from 1990 to 1996, identified patients who had a minimal follow‐up of two years after removal of adenomatous polyps isolated to the rectosigmoid. Polyps detected on surveillance colonoscopy were categorized as distal (≤60 cm from anal verge), proximal (>60 cm from anal verge), and diffuse (proximal plus distal). The risk of polyp formation was determined by actuarial analysis using the Kaplan‐Meier method.RESULTS:Sixty‐two patients undergoing surveillance for adenomas met inclusion criteria. At the index colonoscopy, 124 isolated rectosigmoid polyps were identified. The median polyp size was 1 cm and median frequency was one polyp. The median follow‐up time for the entire cohort (N = 62) was 53 months. At follow‐up surveillance colonoscopy, 105 additional adenomas were discovered and removed in 40 patients. No malignant polyps were detected. The pattern of polyps detected were proximal (n=19), rectosigmoid (n=16), and diffuse (n=5).CONCLUSIONS:The majority (65 percent) of patients with isolated rectosigmoid polyps have additional polyps on long‐term surveillance, and 60 percent of patients will have these polyps located proximal to the reach of a sigmoidoscope. Therefore, flexible sigmoidoscopy is not a safe alternative for surveillance of patients with isolated rectosigmoid polyps.