A colonoscopy and colonoscopic polypectomy service was established at Wellington Hospital, New Zealand in April 1975. Between April 1975 and March 1990 1157 polyps were either removed or biopsied and examined histologically. Twenty-five polyps were lost. Patient-age seemed to increase through the spectrum hyperplastic, tubular, tubulovillous, villous, and polypoid carcinoma. Sessile < 6 mm in diameter hyperplastic polyps were more numerous than small adenomatous polyps. Pedunculated tumours were most commonly adenomata in all sizes, whereas sessile tumours in the rectum and sigmoid colon were usually hyperplastic. As polyp size increased the numbers of hyperplastic polyps decreased relative to the numbers of adenomatous polyps. The majority of hyperplastic polyps were found in the distal colo-rectum. Site distribution for hyperplastic polyps corresponded to the site distribution for colorectal carcinomata. One of five patients with hyperplastic index polyps was found to have an adenomatous polyp at follow-up. Strong evidence for a sequential relationship between hyperplastic and adenomatous polyps was not found in this study. It is unlikely that an aggressive attitude to the investigation and removal of hyperplastic polyps will have a significant effect on the later development of colorectal cancer.