Background: DCIS-components of invasive breast-cancers are a major cause for positive margins and reoperations in women undergoing breast-conserving-surgery. We investigated whether breast-MRI, through improved diagnosis of such DCIS-components, combined with MR-guided needle biopsy and pre-operative MR-guided lesion bracketing where appropriate, would help reduce reoperation-rates for invasive breast cancers. Our hypothesis was that with improved diagnosis of local disease extent through MRI and MR-guided surgery, reoperation rates should be low, and should be independent of the presence or absence of a DCIS-component. Methods: Prospective study in two academic breast-centers on consecutive patients with newly-diagnosed invasive breast-cancer. Women underwent breast-MRI in addition to conventional imaging (CI; digital-mammography/breast-ultrasound), and MR-guided needle-biopsy and preoperative MR-guided lesion bracketing where appropriate. Accuracy of breast-MRI for diagnosing DCIS-components was compared with that of CI, stratified by nuclear-grade and relative size of DCIS-components. Surgical outcomes (reoperation and mastectomy-rates) were recorded, stratified by presence or absence of DCIS-components. Results: 593 women were included. Surgical-pathology documented DCIS-components in 139/593 (23.4%) women. Sensitivity of MRI (84.9%) for demonstrating DCIS-components was significantly higher than that of CI (36.7%) (p < 0.0001); over half (51.1%) of DCIS-components were only detected by MRI. The sensitivity advantage of MRI over CI increased significantly with increasing relative size and nuclear-grade of the DCIS-component. Reoperation-rates were equivalent for women with vs. without DCIS-components (10.1% vs. 9.9%); mastectomy rates were 10.8% and 8.1%, respectively. Similar Positive-Predictive-Values were achieved with CI and MRI. Conclusions: Breast-MRI significantly improves depiction of DCIS-components of invasive breast-cancers prior to surgery. Use of breast-MRI and MR-guided surgery translates into low reoperation rates for women with operable invasive breast-cancer, which were similar for women with or without DCIS-components.