It has been suggested that colorectal cancer might not be one homogenous disease entity, based on the distinctive characteristics of its subsite of origin. Incidence data on 4,987 colorectal cancer were obtained from the Seoul Cancer Registry between 1993 and 1995. Age, sex, and subsite-specific incidence rates were compared. The age-standardized annual incidence rates of total colorectal cancer were 26.1 and 18.0 per 100,000 for men and women, respectively. There were no appreciable difference in the rates of colon and rectal cancer for either sex (colon vs rectum: 12.8 vs. 13.2 for men, 9.3 vs. 8.6 for women). The incidence rate of right colon was slightly higher in men than in women, and this discrepancy became even greater in left colon (men vs women: 3.5 vs. 3.0 for right colon, 4.7 vs. 2.9 for left colon). When the incidence rate of right colon was compared with that of left colon, women had a higher rate in the right colon among the elderly, aged 60 yr and over and a lower rate at age 40 yr or less, while the opposite was observed for men. More analytic approaches are needed to identify which factors are related with these descriptive results in colorectal cancer incidence.