Ten of 152 (7%) consecutive breast cancer patients who underwent excisional biopsy and radiation therapy developed suspect microcalcifications at the biopsy site. All ten patients underwent reexcision. Seventeen other patients developed scattered, coarse, benign macrocalcifications that have remained stable as determined with mammographic follow-up. Of the ten patients who underwent reexcision, six had clusters of calcifications that were benign, and four had malignant calcifications. The morphologic appearance of the microcalcifications was similar in both malignant and benign disease, although the malignant calcifications tended to appear earlier than the benign ones. Three of the four patients with recurrent carcinoma had had calcifications in the original cancer. The mammographic features of the microcalcifications were not specific enough to distinguish recurrent malignancy from benign disease. Unless calcifications that occur in the breast after lumpectomy and radiation therapy have an unequivocally benign appearance (ie, scattered, round, homogeneous-appearing macrocalcifications), they should be viewed with suspicion and subjected to excisional biopsy.