The number of surgeries for colorectal cancer in elderly patients is increasing in correspondence to Japan's aging society. It is important to evaluate the patient's condition in order to carry out operations safely. The Onodera index (Onodera index in order (PNI: prognostic nutritional index)=serum alb value × 10+the lymphocyte counts of peripheral blood) is a simple and useful tool for choosing the method of operation. In our experience, 75% of elderly patients had pre-operative complications. Respiratory and circulatory complications occurred more frequently after operations. Pre- and post-operative adequate management can help facilitate a safer operation. Even if a curative operation was carried out for an elderly patient, both the cancer-specific survival rate and the 5-year relative survival rate were good. If the operation is tolerable for the elderly patient, curative resection should be performed. Chemotherapy in elderly should be also evaluated by the patient's activities of daily living and the regimen of chemotherapy should be selected.