During an 18-mo period, 760 palpable mammary lesions were examined and aspirated. When indicated, mammography was performed in addition. Three separate aspirations were performed in each lesion utilizing 23 gauge (0.6 mm) needles. Biopsies were performed following aspiration in 206 lesions; and 470 of the cases in whom biopsies were not performed were followed up clinically for periods of 10 to 26 mo (mean period 15 mo). Accuracy and sensitivity of the cytological examination were found to be far higher than that of clinical evaluation or mammography. Aspiration cytology resulted in only 1.5% false negative, no false positive, and only 1.65% inconclusive reports. On the other hand, clinical evaluation and mammography yielded 35 and 29% false negative, 0.3 and 0.8% false positive, and 6.75 and 8.8% inconclusive findings, respectively. Eleven malignant cases that were considered to be benign both clinically and mammographically, were correctly diagnosed cytologically. Aspiration cytology was found to be the most accurate of the preoperative diagnostic methods.