The clinicopathologic features of a malignant fibrous histiocytoma arising in a female breast are presented. Seven cases have been previously reported. These may be divided into three subgroups based on history and pathologic findings. Three of the seven occurred in women without a history of other tumors or previous irradiation. One appeared with a cytosarcoma phyllodes, and three arose following radiation for carcinoma of the breast. The patient in this study had received no radiation. Treatment has been based on surgical resection; the roles of chemotherapy and radiation are uncertain. Although resection alone in the first subgroup has lead to no reported mortality, the small number of cases and the relatively short follow-up does not allow a meaningful assessment of the prognosis in this disease.