A retrospective review of 922 colorectal cancer patients was undertaken to determine whether the nonuniform anatomic distribution of colorectal cancer was influenced by age and/or sex. The mean age of patients with right colon lesions (71.2 years) was significantly higher than for either patients with left colon lesions (68.2 years) or rectal lesions (65.6 years). Further analysis disclosed that patients with proximal tumors were older than patients with distal tumors primarily because of the later presentation of females with cecal or ascending colon cancers. Comparison of the anatomic distribution of tumors in patient groups above and below the age of 70 revealed that right colon cancers accounted for a greater percentage of colorectal tumors in the older patient group than in the younger patient group. These findings support the roles played by both age and sex in influencing colorectal cancer location. Furthermore, these data provide a plausible explanation for the increasing incidence of proximal colonic lesions.