In patients with primary breast cancer, preoperative MRI identifies additional foci of tumor in the ipsilateral or contralateral breast that are not evident with standard imaging. Breast cancer patients who are otherwise deemed suitable candidates for breast-conserving surgery might, therefore, be urged to undergo mastectomy or even bilateral mastectomy following staging with preoperative breast MRI. The effect of preoperative breast MRI on clinical end points (rates of ipsilateral breast tumor recurrence) and surgical end points (rates of reoperation) have been assessed in several large studies. These studies indicate that the routine use of preoperative breast MRI is not beneficial. The additional occult foci of tumor detected with preoperative breast MRI seem to either have no clinical significance, or can be adequately treated with radiotherapy and/or systemic therapy. This article reviews these studies and highlights the potential harms associated with the routine use of preoperative MRI in patients with primary breast cancer.