In 70 selected patients with suspect breast lesions at mammography, accurate, high-speed stereotaxic core-cut biopsy (SCCB) was performed with a biopsy gun. In 17 of the patients, no surgery was performed. The results of SCCB were normal in 11 of these patients; in six patients, the lesion disappeared after SCCB. In 53 of the patients, SCCB was followed by surgical biopsy. In 48 cases (91%), the results of SCCB and surgical biopsy were concordant. Of the 45 carcinomas found at surgery, 41 (91%) were correctly diagnosed with SCCB. There were no false-positive results. SCCB was nondiagnostic (no representative material sampled) in three patients (6%), and in two patients (4%) a false-negative result was obtained. The infiltrating character of the tumor was correctly diagnosed with SCCB in 80% of cases. These results confirm that this radiologic procedure is an acceptable alternative to excisional biopsy.