We describe a patient in whom angiosarcoma developed at the site of a hemangioma that was treated during infancy with radiation for refractory thrombocytopenia. Our findings, along with those of the 10 reported cases from the world literature, are summarized. One third of angiosarcomas arise in the skin. They most often show one of three clinical patterns. First and most common is occurrence as a bruiselike lesion on the scalp or face of an elderly person. Second in frequency is the Stewart-Treves syndrome. Third and least common is angiosarcoma developing as a sequela of previous radiation therapy. The prognosis in general is poor, with a mean survival length of 24 months and a 5-year survival rate of 10%. Effective treatment relies on early diagnosis and wide-margin surgical excision.