During a 5-year period, 28 women who had been treated conservatively for breast carcinoma had 29 reexcisions of the lumpectomy site because of suspicion of a recurrent malignant tumor. Biopsy results were benign in 19 cases and malignant in 10 cases. Sixteen of the 19 benign tumors had developed within 2 years after therapy. In 16 benign cases, a palpable lump developed at the scar and was found on biopsy to be fat necrosis or fibrosis. Seven of these cases had normal mammographic findings. Three women with abnormal mammographic findings but a normal breast examination had punctate microcalcifications develop at the scar; these were due to fibrosis in two and sclerosing adenosis in the other. Of the 10 malignant recurrent tumors, seven were palpable, four of which also were identifiable by mammography. Of seven mammographically identifiable recurrent tumors at the surgical site, four were palpable. Mammographic findings were a single mass in two cases, multiple masses in one, microcalcification in three, and a mass with microcalcifications in one. Malignant microcalcifications were all linear, irregular, and in one case branching. Mean time to recurrence in these 10 women was 3 years. This experience suggests that benign disease usually occurs at the scar within 2 years after the original therapy and when palpable may not show changes on mammography. When microcalcifications do occur, they are usually punctate.