One hundred fifteen patients underwent needle aspiration biopsy of palpable breast masses prior to open biopsy. Aspirates were obtained by surgical residents, prepared by a cytotechnologist present at the procedure, and evaluated by a single pathologist. Cytologic findings were interpreted as positive or highly suspicious for malignancy, normal or benign, or insufficient. All patients underwent open biopsy. Patients with positive or highly suspicious cytologic findings who preferred partial mastectomy and radiotherapy were offered a segmental mastectomy. No patient was offered total mastectomy based on cytologic findings alone. There were two false-positive and two false-negative results, for a 92 percent sensitivity and 97 percent specificity. The value of needle aspiration biopsy lies in its ability to identify patients at high risk for malignancy. Total mastectomy cannot be recommended based on cytologic findings alone. The setting of a surgical residency program does not adversely affect the reliability of the technique.