Breast core biopsy is one of the major nonoperative methods of diagnosis. Increasingly, there is also a need to provide prognostic data to facilitate timely patient management. We present the results from 500 patients with invasive breast carcinoma, who underwent core biopsy followed by a therapeutic surgical procedure. Grade and type of the invasive and in situ carcinoma, together with the presence or absence of vascular invasion, were determined in both biopsy and definitive surgical excision and the results compared. There was 67% agreement with overall grade (kappa value 0.48), with scores for tubule formation, pleomorphism, and mitotic scoring achieving values of 82%, 73%, and 58%, respectively. Only 60% of grade 1 and 2 carcinomas showed concordance, but 84% of grade 3 tumors showed agreement between core and excision results. Tumor typing, vascular invasion, and grading of ductal carcinoma in situ had agreement values of 74%, 69%, and 65%, respectively. The major problem with assessing prognostic factors on needle biopsy specimens is undersampling of the most informative areas. However, in those patients in whom preoperative assessment of prognostic factors is most likely to be beneficial, i.e., those with grade 3 carcinomas, a high level of agreement was achieved in this large study.