A study of ten cutaneous angiosarcomas is presented. These tumors characteristically involve the scalp or face of elderly individuals, where they present as bluish or violaceous plaques and nodules. They have a marked tendency for local spread in surface and depth, and a third of them eventually give rise to distant metastases, particularly to cervical lymph nodes and lung. Microscopically, angiomatous areas of freely anastomosing channels lined by atypical endothelial cells are seen alternating with Kaposi-like spindle cell areas and undifferentiated foci. By electron microscopy, the tumor cells are seen to have all the features of endothelial cells, including pinocytotic vesicles, tubulated bodies, and in one case closed fenestrations. They also exhibit a cytoplasmic specialization here interpreted as the intracellular formation of a vascular lumen. Pericytes and cells resembling smooth muscle cells are also present. In the differential diagnosis this entity has to be distinguished from other clinical types of angiosarcoma of the skin and from a number of benign and malignant conditions. It is suggested that surgery be used for solitary, well circumscribed tumors and radiation therapy for tumors that either are multicentric or have ill defined margins.