Over the past 20 years, multiple international clinical studies have shown equivalent survival between patients treated with modified radical mastectomy and appropriately selected patients treated with breast-conserving surgery and adjuvant radiation, hormonal therapy, and chemotherapy. Accordingly, breast-conserving surgery has become the dominant mode of treatment, with modified radical mastectomy becoming the alternate choice in certain circumstances. A residual large cancer after adjuvant therapy (especially in a small breast), multicentric cancers, and patient preference or concerns about the complications of radiation therapy are the principal indications for the operation. Prior to surgery, the opposite breast should be evaluated by physical examination and mammography. Appropriate blood tests and imaging scans and mammographic studies are made in a search for potential metastases to the lung, liver, or bone. The standard preadmission physical examination and laboratory evaluations are done in an ambulatory setting, as most patients are admitted to the hospital on the day of operation.