In order to identify an adeqauate surgical treatment for elderly gastric and colorectal cancer patients, clinicopathological features and surgical results of the patients over 80 years of age were compared with those of patients between 75 and 79. Although more invasive procedures were performed for patients between 75 and 79, postoperative complications were higher in gastric cancer patients over 80 (94.7%) than in those between 75 and 79 (64.9%) (p<0.05). The incidence of postoperative pulmonary complications was higher in gastric cancer patients over 80 (73.7%) than in those between 75 and 79 (37.8%) (p<0.05). In colorectal cancer, complications which were not directly related to operative methods, i.e., pulmonary complications, occurred frequently in patients over 80. The cumulative survival rate was lower in patietns over 80. In particular, the prognosis of the patients over 80 with postoperative pulmonary complications was poor. The number of dissected lymph nodes and the incidence of combined resection of other organs were higher in the gastric cancer patients with postoperative pulmonary complications, and multiple proce-dures extending to the upper abdomen were frequently performed for colorectal cancer patients with pulmonary complications. These results suggest that radical lymph node dissection and combined resection of other organs in the treatment of aged patients with gastric cancer, and multiple procedures extending to the upper abdomen in aged colorectal cancer patients, should be minimized to prevent postoperative complications and improve the prognosis.