Postoperative mortality from colorectal cancers in the resident population of the department of Côte-d'Or was studied for the 1976-1985 period through the data collected by the Registry of Digestive Tumors of the Côte-d'Or (France). The overall postoperative mortality was 14.7 percent for colonic cancers and 11.2 percent for rectal cancers. After surgery with curative intent (n = 1,411), the corresponding figures were 10.3 percent and 6.8 percent, respectively. In patients operated with curative intent, postoperative mortality was slightly less in females than in males (NS), and in patients less than 65 than in older patients (P less than 0.001). It was higher when cancer was discovered through an acute event (20.0 percent) than in the other patients (7.7 percent; P less than 0.001). Stage at diagnosis, gross macroscopical appearance, and tumour size had no influence on postoperative mortality for colonic cancers. For rectal cancers, postoperative mortality was lower in tumors less than 3 cm in diameter (1.3 percent) than in larger tumors (7.5 percent; P less than 0.05). Postoperative mortality decreased by a mean of 9.7 percent per year between 1976 and 1985 (P less than 0.001). This trend was more pronounced after curative surgery: 10.9 percent (P less than 0.001) than after palliative surgery: 5.5 percent (P less than 0.05). After curative surgery, postoperative mortality decreased more in men (annual variation: 13.9 percent; P less than 0.001) than in women (6.3 percent; NS), before age 75 (20.2 percent; P less than 0.001) than in older patients (5.6 percent; NS), and for colonic cancers (13.1 percent; P less than 0.001) than for rectal cancers (9.1 percent; NS).(ABSTRACT TRUNCATED AT 250 WORDS)