Ninety-two patients with resected adenocarcinomas of the rectum, rectosigmoid, or sigmoid, Gunderson Stages B2-3 and C1-3, received postoperative pelvic irradiation between 1976 and 1981. Thirty-three patients had gross or microscopic postoperative residual disease. Half were age 65 or older. Eighty-four patients (92%) completed therapy as planned with 71% given at least 5000 cGy. There were treatment interruptions in 26% but only two complications. The median follow-up was 32 months. Nineteen of 92 recurred in the pelvis (21%): 6/29 (21%), in Stages B2-3 (node -), 13/63 (21%), in C1-3 (node +), 7/50 (14%), in B2, C1-2 (mobile), and 12/41 (29%), in B3, C3 (fixed). There were 10/33 (30%) pelvic recurrences with postoperative residual disease compared to 9/59 (15%) recurrences in completely resected patients (p = 0.1). Among 51 patients who received greater than or equal to 4500 cGy pelvic irradiation, with no residual disease, only five recurred: 1/15 (7%) in B2-B3, 4/36 (11%) in C1-3, 4/38 (11%) in B2, C1-2, and 1/13 (8%) in B3, C3. In this cohort, the 5-year relapse-free survival rates were 83% in Stages B2-3, and 27% in Stages C1-3 (p = 0.023). High dose, postoperative pelvic irradiation is an effective and well tolerated adjuvant for local control of pelvic colon adenocarcinoma.