The risks and benefits of surgery for colorectal cancer in old patients have not been unequivocally defined. The present investigation was carried out in 309 hospitals as a prospective multicenter study. In the period between 1 January 2000 and 31 December 2001, a total of 19,080 patients were recruited for the study; 16,142 (84.6%) patients were younger than 80 years (<80) and 2932 (15.4%) were 80 years and older (> or =80). Significant differences between the age groups were observed for general postoperative complications (22.3% for <80 years; 33.9% for > or =80). Specific postoperative complications were identical in both groups. Overall, significantly elevated morbidity and mortality rates were found with increasing age (morbidity: 33.9% vs. 43.5%; mortality: 2.6% vs. 8.0%). The distribution of tumor stages revealed a significantly higher percentage of locally advanced tumors in the older age group (stage II: 28.0% vs. 34.4%). In contrast, no increase in metastasizing tumors was found in the older age group (stage IV: 17.4% vs. 14.1%). Logistic regression showed that, in concert with a number of other parameters, age is a significant influencing factor on postoperative morbidity and mortality. The increase in postoperative morbidity and mortality rates associated with aging is a result of the increase in general postoperative complications, in particular, pneumonia and cardiovascular complications. Age as such does not represent a contraindication for surgical treatment. The short-term outcome and quality of life are of overriding importance for the geriatric patient.