BACKGROUND: Efforts directed at early detection of breast cancer have resulted in an increased incidence of nonpalpable mammographic lesions that warrant excisional biopsy. The most common localization method is by use of the hook wire technique, or needle localization biopsy. Although much has been written about the localization technique, the impact of the method of anesthesia on the accuracy of the biopsy and especially on the completeness of the excision has not been clarified. PATIENTS AND METHODS: We studied 450 needle localization breast biopsies to determine whether the type of anesthesia (local versus general) influenced the accuracy and completeness of the biopsy. We compared 153 biopsies performed under local anesthesia to 297 done under general anesthesia. RESULTS: The use of local versus general anesthesia did not affect accuracy; however, it did determine the inability to achieve clean margins (27.6% versus 7.3%, respectively, P <0.02). It was more difficult to excise completely specimens located deeper than 3 cm in the breast, when the localizing needle travelled more than 3 cm, and when the lesions were of the microcalcification mammographic pattern. CONCLUSIONS: For lesions mammographically suspicious for malignancy, mainly those located deeper than 3 cm, general anesthesia is preferred.