The objective of this study was to assess whether preoperative breast magnetic resonance imaging (MRI) combined with conventional breast imaging techniques decreases the rates of margin involvement and reexcision.Data on patients who underwent surgery for primary operable breast cancer were obtained from the Changhua Christian Hospital (CCH) breast cancer database. The rate of surgical margin involvement and the rate of reoperation were compared between patients who underwent conventional breast imaging modalities (Group A: mammography and sonography) and those who received breast MRI in addition to conventional imaging (Group B: mammography, sonography, and MRI).A total of 1468 patients were enrolled in this study. Among the 733 patients in Group A, 377 (51.4%) received breast-conserving surgery (BCS) and 356 (48.6%) received mastectomy. Among the 735 patients in Group B, 348 (47.3%) received BCS and 387 (52.7%) received mastectomy. There were no significant differences in operative method between patients who received conventional imaging alone and those that received MRI and conventional imaging (P = 0.13). The rate of detection of pathological multifocal/multicentric breast cancer was markedly higher in patients who received preoperative MRI than in those who underwent conventional imaging alone (14.3% vs 8.6%, P < 0.01). The overall rate of surgical margin involvement was significantly lower in patients who received MRI (5.0%) than in those who received conventional imaging alone (9.0%) (P < 0.01). However, a significant reduction in rate of surgical margin positivity was only observed in patients who received BCS (Group A, 14.6%; Group B, 6.6%, P < 0.01). The overall BCS reoperation rates were 11.7% in the conventional imaging group and 3.2% in the combined MRI group (P < 0.01). There were no significant differences in rate of residual cancer in specimens obtained during reoperation between the 2 preoperative imaging groups (Group A, 50%; Group B, 81.8%, P = 0.09). In multivariate analysis, multifocal/multicentric breast cancer (odds ratio = 2.38, P = 0.02) and without MRI use (odds ratio = 2.35, P < 0.01) were the major predisposing factors to margin involvement in patients received BCS.Preoperative breast MRI combined with conventional breast imaging results in a lower rate of surgical margin involvement and reoperations in patients who receive BCS.