PURPOSE: Circumferential resection margin (CRM) involvement is a prognostic factor for local recurrence in rectal cancer. In a randomized trial comparing preoperative radiotherapy (5 x 5 Gy), followed by total mesorectal excision (TME) with TME alone, we demonstrated the beneficial effect of short-term preoperative radiotherapy on local recurrences. Here we evaluate the effect of radiotherapy on local recurrence rates in patients with different CRM involvements. METHODS AND MATERIALS: Circumferential margins were defined as positive (2 mm). Postoperative radiotherapy was mandatory for surgery-only patients with a positive CRM, but was not always administered and enabled us to compare local recurrence rates for patients with or without postoperative radiotherapy. Furthermore, the effect of preoperative radiotherapy was assessed in the different margin groups. RESULTS: Of 120 patients in the surgery-only group with a positive CRM, 47% received postoperative radiotherapy. There was no difference in the local recurrence rate between the irradiated and nonirradiated patients (17.3% vs. 15.7%, p = 0.98). Preoperative radiotherapy was effective in patients with a narrow CRM (0% vs. 14.9%, p = 0.02) or wide CRM (0.9 vs. 5.8%, p