UNLABELLED: A prospective study was lead in order to analyze the accuracy of an X-ray device settled in the operating room for margin assessment, when performing breast-conserving surgery. PATIENTS AND METHODS: One hundred and seventy patients were included. All lesions were visible on the preoperative mammograms. An intraoperative X-ray of the lumpectomy specimen was systematically performed for margins assessment. Final histological data were collected and the accuracy of intraoperative specimen radiography (IOSR) for margin assessment was analyzed. RESULTS: IOSR allowed an evaluation of margins status in 155 cases (91.2%). After final histological examination, the positive margins rate would have been 6.5% if margin assessment had relied only on IOSR. CONCLUSION: Margin assessment with a two-dimensional X-ray device would have allowed the achievement of negative margins in 93.5% of the cases. Moreover, this procedure allows important time-saving and could have a substantial economical impact.