As part of the quality assurance role of the Cancer Committee at Barnes Hospital, an institutional audit of Needle Localization Breast Biopsy (NLBB) was performed. Mammographic, operative, and surgical pathology reports from 370 consecutive patients at our institution undergoing both mammography and needle localization biopsy over a 34-month interval were reviewed. Carcinoma was diagnosed pathologically in 103 patients (28%), and 27% of these proved to be noninvasive. Sixteen patients were found to have histologic or clinical involvement of the axillary nodes; no patients with Tis lesions were found to have axillary nodal involvement. Of the patients, 73% were found to have either Stage 0 or Stage I disease, and 61% with an established malignancy had mastectomy (67% of patients with invasive carcinoma, 44% of those with carcinoma-in-situ), whereas 39% had some form of conservation therapy (33% of patients with invasive lesions, 56% of those with carcinoma-in-situ). Our results have been compared with other published studies, and important clinical indicators for evaluating the results of individual centers performing NLBB are discussed. It is concluded that NLBB is a safe and effective method of biopsying nonpalpable breast lesions, which allows for the identification of early stage breast carcinomas. In the present environment of concerns about the quality of care and costs, it is the responsibility of each center performing NLBB periodically to evaluate their results with this multidisciplinary procedure and to bring about change in those areas found to be deficient.