The purpose of this study is to determine whether including breast magnetic resonance imaging (MRI) in the preoperative workup of patients with known breast cancer has an impact on mastectomy and/or re-excision rates. This is an Institutional Review Board approved HIPAA compliant retrospective study reviewing the impact MRI has on mastectomy and re-excision rates in patients with newly diagnosed breast cancer. Our study compares two groups: (i) 154 patients who did not receive preoperative MRIs and served as a control group and (ii) 96 patients who received preoperative breast MRIs. Patient race and age between the two populations were not statistically different. The difference in mastectomy rates between the two populations was 10.7%; although not statistically different, the p value of 0.10 suggests a trend toward significance. The re-excision rates between the two populations, however, were significantly different (p < 0.001), with women in the control group having a higher re-excision rate than those in the study group. The difference between involved and clear margins was significant as well (p = 0.002), with patients undergoing preoperative MRI more likely to have negative margins. Preoperative breast MRI significantly decreases the likelihood of involved margins as well as the need for surgical re-excision. Preoperative breast MRI does not result in a statistically significant difference in mastectomy rates, although further investigation is required to determine whether there is a trend towards statistical significance.