Radiation therapy plays an important role in the treatment of patients with colorectal cancer. Randomized trials show that patients with rectal cancer have an 8% improved local control rate with postoperative radiation and an 11-13% improved local control rate with combined postoperative radiation and chemotherapy. Survival is also improved for these patients. Ongoing randomized trials may clarify the role of postoperative radiation therapy for patients with colon cancer. Although there is little specific information regarding the tolerance and response of the older patient to radiation therapy, there is no reason to believe that cancer in the older patient is more sensitive to ionizing radiation. Therefore, treatment decisions should be based on the available data. The older patient may be at an increased risk for radiation-related small bowel damage, and the clinician should pay particular attention to techniques to limit the amount of small bowel in the irradiated field.