An image-guided core-needle breast biopsy (IGCNBB) diagnosis of ductal carcinoma in situ (DCIS) is often upgraded to invasive carcinoma (IC) after complete excision. When IC is identified after excision patients must be returned to the operating room for evaluation of their axillary nodes. We performed this study to identify histologic or mammographic features that would predict the presence of invasion when DCIS is documented by IGCNBB. Patients with an IGCNBB diagnosis of DCIS were identified from a prospective database. Imaging abnormalities were classified as either calcification only or mass with or without calcifications. IGCNBB specimens were reviewed to document nuclear grade and the presence of comedo-type necrosis, periductal fibrosis, and periductal inflammation. Patients were divided into two groups, DCIS and IC, on the basis of the final diagnosis after complete excision. From July 1993 through May 2000, 148 of 2995 (4.9%) IGCNBBs demonstrated DCIS; eight were excluded after pathologic review. Of the remaining 140 patients 36 (26%) demonstrated IC after complete excision. The presence of a mass on breast imaging was the only significant predictor of IC (P = 0.04). On the basis of the results of this study we now perform sentinel lymph node mapping and biopsy at the initial surgical procedure for patients with an IGCNBB diagnosis of DCIS and an associated mass on breast imaging.