Radiation therapy (RT) plays an important role in the management of patients with rectal cancer. However, there is mounting evidence that RT results in functional changes. The purpose of this study was to review the published data on bowel and sexual functional changes associated with RT and to determine the optimal strategy. The data suggest that studies are generally small, retrospective studies, use various RT regimens, and assess function with various nonstandardized parameters. In general, bowel function as measured by frequency, urgency, evacuation, sensation, and/or continence is impaired after RT when compared with patients not treated with RT. Although limited, preoperative RT tends to cause less impairment than postoperative RT. Sexual function is poorly studied, but data suggest that RT has a negative impact in both men and women. Further study is necessary to understand the extent of impairment, optimize radiation strategies, and select patients who will gain the most with RT.