Defining the role of subtotal colectomy in the treatment of carcinoma of the colon. Seventy-two patients with colon cancer were treated by primary subtotal colectomy, including 23 patients with acute and subacute left colon obstruction. There were two operative deaths and no cases of disabling diarrhea. One death occurred in the group with colon obstruction. Other indications for subtotal colectomy included multiple polyps associated with the primary tumor (32), synchronous carcinomas (15), a previous transverse colostomy for obstruction (8), associated severe sigmoid diverticular disease (2), age less than 50 years with a positive family history (3), adherence of the sigmoid loop to a cecal tumor (2), and metachronous carcinoma (2). There were multiple indications in several patients. Subtotal colectomy has a defined role in a wide variety of clinical settings associated with colon cancer, including management of obstruction of the left and sigmoid colon, particularly if the proximal colon cannot be evaluated before operation by colonoscopy or barium enema. Segmental or regional colonic resections are appropriate if the entire colon can be evaluated before operation and no associated neoplasms are revealed. 