Despite the widespread use of radiation therapy to treat breast carcinoma, angiosarcomas arising in the field of radiation therapy are rare. The authors studied three patients with cutaneous angiosarcoma and four patients with atypical vascular lesions (AVL). All had breast conserving surgery, axillary lymph node dissection, and radiation therapy for breast carcinoma. Six patients received conventional high energy postoperative doses of external beam radiation therapy to the breast. Details of radiation therapy were not available for one angiosarcoma patient. Angiosarcoma was diagnosed 3.5 years, 3.7 years, and 5.25 years after radiotherapy. The three angiosarcomas were multifocal or diffuse and high grade, with solid cellular foci located mainly in the dermis. In three patients AVL presented as discrete skin nodules (2 unifocal and 1 multifocal) and in one patient as a breast mass. The four AVL consisted of focal proliferation of dilated vascular spaces lined predominantly by a single layer of plump and sometimes hyperchromatic endothelial cells. After two angiosarcoma patients underwent mastectomy, one died 10 months after diagnosis with recurrent local angiosarcoma and the other is alive without angiosarcoma 2 months after diagnosis. One angiosarcoma patient died of unrelated causes 2 weeks after diagnosis. One AVL patient developed a second cutaneous AVL in the axillary region 17 months after excision of an AVL from the same area. None of the AVL patients has developed angiosarcoma or recurrent mammary carcinoma. They remain well 10 months, 18 months, 7 years and 7 months, and 10 years, respectively, after initial local excision. The authors conclude that cutaneous angiosarcoma and unusual benign cutaneous vascular lesions can develop within the field of radiation therapy for breast cancer. Unlike other radiation therapy-induced sarcomas, cutaneous angiosarcoma often occurs within a short time interval after radiotherapy. It is important to distinguish AVL from angiosarcoma. Longer follow-up will be necessary to fully characterize the prognostic importance of atypical vascular lesions, but currently there is no evidence that they represent a precursor to radiation-induced angiosarcoma.