BACKGROUND/AIMS: Several lines of evidences suggest that the distribution of colorectal adenomatous polyps are different according to age and gender. Therefore, the efficacy of screening sigmoidoscopy for colorectal cancer not considering age and gender necessitates reappraisal. We aimed to evaluate the distributions of colorectal adenomatous polyps according to age and gender. METHODS: Total of 1,886 patients (1,322 men, 564 women) who underwent colonoscopy at Severance hospital, Seoul, Korea between July 1995 and September 2002, were included. The proximal colon was defined as the colon proximal to the sigmoid-descending junction. The advanced polyp was defined as the adenomatous polyp with one or more of the following features: (1) 1 cm or larger in diameter, (2) villous histology, (3) high grade dysplasia or adenocarcimoma. RESULTS: The risk of adenomatous polyps in the proximal colon was higher in men than women (OR, 1.63; 95% CI, 1.33~1.99, p < 0.05), and increased with age (p < 0.05). The risk of advanced polyps in the proximal colon tended to be higher in men than women, and to increase with age, but did not reach statistical significance. Among 1,886 patients with colorectal adenomatous polyps, 587 patients (31.1%) had polyps only in the proximal colon. Among 814 patients with advanced colorectal adenomatous polyps, 217 patients (26.7%) had advanced polyps only in the proximal colon. The risks of adenomatous polyps or advanced polyps found only in the proximal colon were not different according to sex, but tended to increase with age. CONCLUSIONS: The risk of adenomatous polyps in the proximal colon was higher in men compared to women and increased with age. About one third of the patients with colorectal adenomatous polyps had polyps only in the proximal colon. Colonoscopy is a better strategy for endoscopic screening for colorectal cancer compared with sigmoidoscopy, especially, in elderly male.