Thirty-one cases of malignant mesenchymal tumors of the breast were analyzed with the purpose of identifying the most suitable type of surgery to be recommended. All the cases considered underwent pathologic review. Even young women were affected, and menopausal status did not seem to influence the development of mesenchymal tumors. Mammography was of little use for diagnosis. All cases underwent surgery and 26 had an adequate follow-up. In 8 cases a relapse occurred with a mean free interval of 6 months. Total mastectomy was sufficient to provide local control, whereas axillary dissection turned out to be not worthwhile. Postoperative radiotherapy did not improve distant results. Relapses mainly consisted of lung metastases. Fifteen patients were alive, free of disease, at a time ranging from 9 months to 13 years after surgery.