Despite improved surgical treatment strategies for rectal cancer, 5-15% of all patients will develop local recurrences. After conservative surgery, circumferential resection margin (CRM) involvement is a strong predictor of local recurrence. The consequences of a positive CRM after total mesorectal excision (TME) have not been evaluated in a large patient population. In a nationwide randomized multicenter trial comparing preoperative radiotherapy and TME versus TME alone for rectal cancer, CRM involvement was determined according to trial protocol. In this study we analyze the criteria by which the CRM needs to be assessed to predict local recurrence for nonirradiated patients (n = 656, median follow-up 35 months). CRM involvement is a strong predictor for local recurrence after TME. A margin of