To evaluate the efficacy of ultrasound (US)-guided automated large-core percutaneous needle breast biopsy, biopsy of 181 ultrasonographically suspicious breast lesions was performed by using a long-throw biopsy gun and 14-gauge needles with continuous US guidance. A "freehand" technique with either 5.0- or 7.5-MHz linear-array transducers was used. Needle core diagnoses were compared with surgical diagnoses in the 49 lesions subsequently surgically excised. The remaining 132 cases were followed for 12-36 months. Agreement between needle-core and surgical diagnoses in the 49 lesions was 100%. This group included 34 cancers (28 infiltrating ductal, two mucinous, one mixed infiltrating ductal and lobular, and one each of intraductal, infiltrating lobular, and tubular carcinoma). To date, no cancers have been found in the other 132 cases. The procedure time averaged 20 minutes, and no complications occurred. With an accuracy approaching that of excisional biopsy, US-guided needle core biopsy provides an alternative to surgery.