Objective: The surgical margin status after breast-conserving surgery is considered the strongest predictor for local failure. The purpose of this study is to survey how radiation oncologists in North America (NA) and Europe define negative or close surgical margins after lumpectomy and to determine the factors that govern the decision to recommend reexcision based on the margins status. Methods: A questionnaire was sent to active members of the European Society of Therapeutic Radiation Oncology and the American Society for Therapeutic Radiology and Oncology who had completed training in radiation oncology. Respondents were asked whether they would characterize margins to be negative or close for a variety of scenarios. A second survey was sent to 500 randomly selected radiation oncologists in the United States to assess when a reexcision would be recommended based on surgical margins. Results: A total of 702 responses were obtained from NA and 431 from Europe to the initial survey. An additional 130 responses were obtained from the United States to the second survey regarding reexcision recommendations. Nearly 46% of the North American respondents required only that there be “no tumor cells on the ink” to deem a margin negative (National Surgical Adjuvant Breast and Bowel Project definition). A total of 7.4% and 21.8% required no tumor cells seen at <1 mm and <2 mm, respectively. The corresponding numbers from European respondents were 27.6%, 11.2%, and 8.8%, respectively (P <0.001). Europeans more frequently required a larger distance (>5 mm) between tumor cells and the inked edges before considering a margin to be negative. Conclusion: This study revealed significant variation in the perception of negative and close margins among radiation oncologists in NA and Europe. Given these findings, a universal definition of negative margins and consistent recommendations for reexcision are needed.