To identify factors in breast cancer patients that predict the pathologic results of re-excision for close or positive margins and to determine the effect on local control.We divided 1,044 patients with Stage I-II breast cancer with a close (< or =2 mm) or positive margin after initial excision into three groups. Group 1 included 199 patients without additional excision, Group 2 included 546 patients with re-excision found to be free of cancer, and Group 3 included 299 patients with re-excision and residual cancer. All patients were treated with radiotherapy with a median follow-up of 6.7 years.The 10-year local control rate was 95% for Group 1 and 94% for Groups 2 and 3 (p = 0.788). Of the 846 patients, 65% had no residual disease on re-excision and 35% did have residual tumor. The factors significantly associated with positive re-excision findings were initial positive margins, positive nodes, Stage T2 tumor, and an extensive intraductal component. The 10-year local control rate was 95% for Group 2 vs. 91% for Group 3 (p = 0.038).The low recurrence rates seen in this study suggest that selected patients with non-negative margins, particularly those with a low risk of having residual disease at re-excision, may be treated with radiotherapy.