The results of 500 preoperative radiographically guided localizations for occult breast lesions over a period of more than 5 years are described. Of the total, 117 (23.4%) were found to be malignant. Biopsy was prompted by abnormal calcifications in 41% (203/500) of the cases and by occult masses, areas of architectural distortion, or asymmetry in 59% (297/500). of 74 patients with carcinoma who underwent axillary lymph node sampling, 78% (58/74) were free of metastatic involvement.