Introduction of mammography along with particular attention for the diagnosis and treatment of nonpalpable breast lesions has led to the development of nonresectional biopsies such as mammography-guided core needle biopsy, ultrasound-guided fine needle aspiration cytology, and localization and excisional biopsy. The Advanced Breast Biopsy Instrumentation (ABBI(R)) system, a recently developed device, has made it possible to remove a lesion completely under local anesthesia, thus providing a more reliable and rapid evaluation on an outpatient basis. We studied 159 patients with nonpalpable breast lesions from December 1996 to August 1998. Fifty-nine patients received core needle biopsies and 100 patients received excision with the ABBI system. The ABBI system patients had postexcisional mammography and specimen radiographs to confirm complete excision of the lesions. Pathologists examined permanent section specimens. In cases of malignancy, total mastectomy or reexcision was performed to secure a tumor-free margin. We collected malignant lesions in 23 of 159 patients, of whom 17 had ductal carcinoma in situ (DCIS). Postoperative histopathologic reports showed DCIS in 11 and infiltrating ductal carcinoma (IDC) in 2 among the 13 malignancies proven by stereotactic core biopsy. Among 10 malignancies proven by the ABBI system, there were 6 DCIS, 1 lobular carcinoma in situ (LCIS), and 3 IDC. In seven patients in whom mammography suggested malignancy but core biopsy showed benign lesion, localization and excisional biopsy confirmed DCIS in four of seven patients. The ABBI system is a more reliable and rapid method of evaluating breast lesions compared with stereotactic core biopsy. It is usually done under local anesthesia, minimizing the deformity of the breast. Therefore the ABBI system can be used as a preferred technique over conventional localization and excisional biopsy.