Clinical, light microscopic and immunohistochemical features of four cases of primary malignant fibrous histiocytoma (MFH) of the breast are presented. Twenty-eight cases have been reported previously. We found that the prognosis of primary MFH located in the parenchyma of the breast is comparable to the prognosis of other MFH located superficial to the fascial level. We therefore conclude that simple mastectomy is adequate surgical therapy for MFH located in the breast. The possible beneficial effects of adjuvant therapy need further investigation.