A woman in her 30s presented to our hospital with the chief complaint of a right breast mass after the birth of her first child. She was diagnosed as having right invasive ductal carcinoma of Luminal-B type and T3N3cM0, stage Ⅲc. While undergoing neoadjuvant chemotherapy, she received genetic counseling and underwent genetic testing and was determined to have deleterious BRCA1 and BRCA2 mutations. After completing chemotherapy, she underwent a right total mastectomy and axillary lymph node dissection. Two years postoperatively, she requested to undergo a contralateral risk-reducing mastectomy( CRRM)of her left breast. Therefore, CT and breast MRI were performed to confirm the absence of contralateral lesions and distant metastases, and subsequently, CRRM was performed. Postoperative pathology results showed non-invasive ductal carcinoma lesions at 5 sites. In the case of hereditary breast and ovarian cancer syndrome such as in this study, lesions may be discovered at an early stage by performing risk-reducing mastectomy.