Routine proctosigmoidoscopic examination of 390 patients revealed polyps in 46%, in 38% examined before July 1, 1965, and in 59% of the patients investigated after this date when greater attention was paid to minute lesions. This frequency parallels that of polyps discovered in the recto-sigmoid colon by careful autopsy studies; this frequency exceeds that of polyps reported in association with recto-colon cancer. Polypoid lesions were found almost twice as often in cigarette smokers as in nonsmokers. Patients with arteriosclerotic heart disease also had more polyps than patients without coronary artery disease, but at less than the 5% level of confidence. The incidence of polyp formation in men was not significantly greater than in women. A higher yield on routine proctosigmoidoscopy may be achieved by selecting cigarette smokers at a younger age than nonsmokers and selecting all patients with arteriosclerotic heart disease for this procedure.