Vascular tumors of the breast, with the exception of perilobular hemangiomas, are generally considered to be malignant. The pathologic and clinical features of 40 patients with angiosarcoma of the breast and 12 with other vascular tumors of the breast were reviewed. Three general histologic patterns of growth were identified among the angiosarcomas and were found to correlate closely with prognosis. Whereas 10 of the 13 patients in histologic Group I were alive and free of disease with an average follow-up of nearly 6 years, only two of 16 Group III patients were free of disease, and 14 have died. The six Group II patients had a survival similar to those in Group I. In this series the disease-free survival at 3 years was 41% and at 5 years 33%, much better than that reported in previous reviews of mammary angiosarcoma. The data also indicated that adjuvant chemotherapy, specifically actinomycin D, is effective in some and possibly all patients with angiosarcoma of the breast. The 12 other vascular lesions had distinctly different morphologic features, a benign clinical course, and should probably not be viewed as angiosarcomas. However, total excision of all vascular lesions of the breast is essential in order to determine both the diagnosis and the appropriate therapy.