Conservative treatment of rectal cancer with either full thickness en bloc local excision or endocavitary irradiation provides excellent local control for highly selected early rectal carcinomas. For either approach the selection criteria are similar. An ideal lesion should be: 1) freely mobile; 2) less than 3 cm in diameter; 3) no evidence of extension into the perirectal fat either on digital examination or on transrectal US; 4) no clinical evidence of involved nodes on physical examination of diagnostic studies; 5) the surgical alternative would be an abdominal perineal resection; 6) well or moderately differentiated. External beam radiation therapy can contribute to the results of conservative treatment by improving the chances of controlling subclinical nodal disease in the pelvis as well as by improving the control of disease in the rectum at the margins of the local procedure. For highly selected patients, the local control and disease-free interval is on the order of 90% with either endocavitary radiation or local excision.