For 1704 patients with large bowel cancer compiled by the Armed Forces Central Medical Registry, selected prognostic factors were related to five-year or longer survival. The majority of late deaths (those occurring after five years) resulted from cancer in the descending colon, sigmoid colon or rectum rather than from cancer in the right or transverse colon. For example, among all patients with cancer of the rectum, 15.4% of those with Dukes' B tumors and 10.9% of those with Dukes' C tumors died of rectal cancer between five and ten years after diagnosis. When late survival rates were compared, patients with right and transverse colon cancer (8 deaths/93 at risk) fared significantly better than those with left colon and rectal cancer (33 deaths/171 at risk; P = 0.01). Among patients with left-sided colon and rectal carcinoma, a further significant difference in late survival was found when stage of disease was considered: patients with Dukes' A cancers (3 deaths/47 at risk after five years) fared better than those with Dukes' C cancers (21 deaths/74 at risk) (P = 0.002). For Dukes' B and C stages of disease, patients with left colon and rectal cancer fared worse than those with right and transverse colon lesions after 60 months. Of all patients who died of large bowel cancer after five years, 69% had a recurrence of cancer by 60 months, and most late recurrences were located in the descending and sigmoid colon and in the rectum. These results show differences in survival after five years with respect to both site of cancer in the colon and stage of initial disease. Our findings indicate that many left-sided large bowel cancers have a slowly progressive natural history.