Angiosarcomas rarely develop within a peripheral nerve or a peripheral nerve sheath tumor. We describe an epithelioid angiosarcoma that arose in a benign schwannoma (neurilemoma) of the right thigh in a 65-year-old man who did not have von Recklinghausen's disease. Histologically, the resected tumor was a high-grade undifferentiated sarcoma that was predominantly arranged in solid sheets or nests and composed of epithelioid cells. The endothelial origin of the tumor was suggested by Factor VIII R-ag, Ulex europaeus-I, CD34, CD31, BNH9, and vimentin immunoreactivity, along with the ultrastructural evidence of occasional Weibel-Palade bodies. In this location, epithelioid angiosarcoma should be distinguished from malignant transformation of a schwannoma with epithelioid changes. This observation stresses the importance of immunohistochemical and ultrastructural analysis in the differential diagnosis of vascular tumors with features of epithelioid sarcoma.