In patients with mammographically detected breast lesions, stereotactic-guided core biopsy was studied as an alternative to surgical biopsy. Fifty-two patients with a total of 58 mammographically detected suspicious lesions underwent stereotactic-guided core biopsy (average 4.7 cores per lesion) with a 14-G biopsy gun. The results were correlated with subsequent needle-localized surgical biopsy that was performed immediately after the core specimens were obtained. The core biopsy results correlated with the surgical biopsy in 54 of the 58 lesions (93% agreement), including correct identification of 14 malignancies. No false negative or false positive results occurred using core biopsy to detect cancer. These findings suggest stereotactic-guided core biopsy is an accurate method and an acceptable alternative to needle localization in the diagnosis of mammographically suspicious nonpalpable breast lesions.