The Gastrointestinal Tumor Study Group (GITSG) protocol GI-7175 randomized 227 patients between 1975 and 1980 following complete surgical resection of stages B2 and C rectal adenocarcinoma to four treatment arms: (1) no adjuvant therapy, (2) chemotherapy only, (3) radiotherapy only, and (4) radiotherapy and chemotherapy (combined modality). The results of the study showed an advantage for combined modality treatment over no adjuvant therapy for time to recurrence (p = 0.005) and for survival (p = 0.01). Severe acute toxicity was frequent in the combined modality arm (61%) but late effects, including radiation enteritis, have been infrequent. We conclude that postoperative adjuvant therapy is indicated in certain stages of rectal carcinoma and that the present state of knowledge suggests combined modality therapy.