In order to determine the prevalence of hyperplastic colonic polyps and a possible relationship between colonic hyperplastic and adenomatous polyps, colonoscopies performed in the past 5 years were reviewed retrospectively in 1766 patients. A total of 143 patients had 196 hyperplastic polyps; 403 patients had 702 adenomatous polyps. The percentage of patients having adenomatous polyps in the presence of hyperplastic polyps was 41.3%, compared with 21.2% in the absence of hyperplastic polyps (P < 0.001). The prevalence of adenomatous polyps proximal to the rectum, and cancer was higher (31 and 7%) in patients with only hyperplastic polyps in the rectum, than in patients with no polyps in the rectum (24 and 2%; P < 0.05). The presence of hyperplastic polyps was significantly correlated with the presence of adenomatous polyps after adjustment for age, sex and previous history of adenomatous polyps. The presence of hyperplastic polyps increased the relative risk of adenomatous polyps 1.5 times (95% confidence interval: 1.3-1.8) compared with their absence, when all three variables - age, sex and previous history of adenomatous polyps were equal. These results suggest that hyperplastic polyps may be a marker for adenomatous colonic polyps.