Stereotaxically guided core needle biopsy is an important procedure used to decrease the number of surgical breast biopsies, as well as to decrease the expense, inconvenience, and deformity that can result from surgical biopsies. Use of the technique also can decrease the expense of breast cancer screening programs. Stereotaxic core biopsy (SCB) should not be used to biopsy lesions that would otherwise not undergo biopsy. The radiologist who performs this procedure must understand the implications of the resultant histological diagnosis and be certain that the pathological and radiological findings are concordant. The performance of this procedure by a radiologist is important for accurate positioning and needle placement in the breast, allowing accurate diagnosis, and in minimizing the number of exposures required for the procedure, thereby keeping the radiation dose to the patient at a minimum. In addition to understanding the guidance system used in this procedure, the radiologist also should understand the needles and guns used and be able to select the most appropriate method for each patient. Patients undergoing SCB should be told that, in some instances, surgical biopsy may still be necessary. They should know that major complications are rare but possible. Before initiating an SCB program, the radiologist performing SCB should develop a mechanism for surgical referral of woman who have a complication or an SCB diagnosis requiring surgery. This article describes the accuracy, indications, patient selection, equipment, technique, histological preparation and interpretation, shortcomings, and complications of SCB. Special emphasis is placed on SCB procedures and findings at Memorial Sloan-Kettering Cancer Center.