To ascertain whether preoperative short-term radiotherapy can improve local tumor control and the long-term survival of patients with operable rectal cancer, a prospective randomised trial was performed from 1988 to 1993. Ninety-three patients with rectal cancer were either directly treated with surgery (n = 46) or underwent preoperative radiotherapy with 5 x 3.3 Gy irradiation and operation within 48 h (n = 47). If indicated (T4, UICC stage III) patients also received postoperative irradiation. Comparison of the methods of operation (abdominoperineal amputation versus anterior resection) revealed no significant difference in 5-year survival rate (P = 0.393). Local control of R0-resected tumors was improved after preoperative irradiation (P = 0.08). The 5-year survival rate was significantly higher after preoperative short-term radiotherapy (P = 0.027). Preoperative radiotherapy is not an independent factor according to overall survival (P = 0.078) and local recurrence (P = 0.07). In agreement with the results of other authors the present study indicates improved local tumor control of rectal cancer after preoperative radiation therapy. The 5-year survival rate was significantly better after preoperative radiotherapy than after surgery alone.