Proctosigmoidoscopies (7679) were performed on 6293 patients during a period from 1962-1974. Polyps were observed in 470 patients (7.5%) and cancer was found in 178 patients (2.8%). Patients (129) (2.0%) were observed to have ulcerative colitis. There were 57 patients with melanosis coli, 12 radiation proctitis, 7 amebic colitis, 5 granulomatous colitis, 2 endometriosis coli, 2 carcinoid and 2 intestinal tuberculosis. Thus, 879 out of 6293 patients examined had some forms of disease, an over-all incidence being 14.0%. Biopsies were performed under the proctosigmoidoscopic observation in 82.4% out of 273 patients with polyps during the 6 yr period from 1969-1974 and 105 patients (46.7%) were observed to have adenomatous polyps. The age-specific distribution pattern and incidences of these patients with adenomatous polyps were mostly consistent with those of 178 patients with cancer of the large bowel, which were observed by proctosigmoidoscopy during the 13 yr period from 1962-1974. Etiological correlation exists between polyps of the adenomatous type and cancer of the large bowel.