To define the characteristics of colorectal cancer with regard to site distribution, age, and sex, due to the significantly increased incidence of colorectal cancer in Japan, we investigated 1,205 Japanese patients with colorectal cancer between 1975 and 1994. When we compared site distribution for age and sex in the entire 20-year period, tumors in the proximal colon were more frequent in elderly patients than in young ones (p < 0.05); this tendency was true only for females (p < 0.01), but not for males. The increased incidence of proximal colon cancer in elderly patients was also found in the second 10-year period (p < 0.05). Because elderly patients are characterized by an increasingly high incidence of proximal colon cancer in recent years, more concerted efforts for the early detection of proximal colon cancer, particularly in the elderly, are called for.