The association between rectosigmoid polyps and polyps in the more proximal colon is still a matter of debate, and the need for colonoscopy in patients with rectosigmoid polyps that are detected by flexible sigmoidoscopy is controversial. The aim of this study was to determine whether or not certain characteristics of rectosigmoid polyps are associated with the presence and characteristics of proximal colonic polyps. Seven hundred and twenty-eight patients who underwent total colonoscopy between October 1995 and June 1998 and who had colorectal polyps were retrospectively analyzed. Patients with inflammatory bowel diseases, familial adenomatous polyposis, or any advanced cancer were excluded. The odds ratio (OR) and 95% confidence interval (CI) of prevalence of proximal colonic polyps according to the patients age and sex, as well as the characteristics of rectosigmoid polyps, were calculated. Advanced adenoma was defined as an adenoma larger than 10 mm or an adenoma of any size with villous component, high-grade dysplasia or invasive carcinoma. Among 728 patients with colorectal polyps, 356 patients (48.9%) had polyps only in the rectosigmoid region, 193 patients (26.5%) had polyps only in the proximal colon, and 179 patients (24.6%) had polyps in both the rectosigmoid and proximal colon. In 535 patients with rectosigmoid polyps, the prevalence of proximal colonic polyps, neoplastic polyps and advanced adenomas were 33.4%, 27.3% and 2.9%, respectively. The prevalence of proximal colonic polyps in patients with rectosigmoid polyps was found to be significantly related to the male gender and elderly patients, in addition to the neoplastic histology of the rectosigmoid polyps. However, the prevalence of the proximal colonic polyps was not related to the size, number and shape of rectosigmoid polyps. In 179 patients with both rectosigmoid and proximal colonic polyps, the characteristics of proximal colonic polyps such as size, number and shape were similar to those of rectosigmoid polyps. We recommend total colonoscopic examination in all patients with rectosigmoid adenomas, regardless of the size, number, and shape, especially in elderly males.