PURPOSE: As film-screen mammography became to be used widely, more mammographic abnormalities without palpablemasses were detecte and the need for surgical biopsies increases. We intended to study the mammographic findingsand pathologic diagnosis together with the preoperative localization procedures used in these cases. MATERIALS ANDMETHODS: From Feb. 1987 to Mar. 1993 localization of breast lesion using Breast Needle/Wire Localizer was done in179 cases. All cases were proven pathologically through surgical biopsy. RESULTS: In these cases,microcalcification(52.0%), mass(29.6%), architectural distortion(2.2%), or combination of the above(16.2%) wasobserved on film mammogram, Most frequent lesion site was upper outer quadrant(53.1%), followed by upper innerquadrant(25.7%), subareolar area(7.8%), lower outer quadrant(6.7%) and lower inner quandrant(6.7%) in decreasingorder of frequency. Cranial(85.5%) approach for needle localization was mostly used but other approaches such ascaudal(5.6%), lateral(5.0%) and medial(3.9%) were also used. A total of 24 cases was malignant(13.4%), and amongthem there were 14 cases of intraductal carcinoma, 1 intralobular carcinoma, 8 invasive ductal carcinoma and 1invsive lobular carcinoma. CONCLUSION: With the use of Breast Needle/Wire Localizer, safe, simple and preciselocalization of non-palpable breast lesion can be achieved. It makes breast biopsy possible with minimal resectionof breast tissue therfore minimizing disfigurement of the breast resullting from operation.