A case of type 1 infantile hemangioendothelioma of the liver in a 3 month old male infant who had an abdominal mass incidentally noted at 40 days of age, is described. Grossly, the tumor showed a well circumscribed, pinkish gray and gelatinous mass with areas of central necrosis, multifocal thrombi and hemorrhages, and small cysts. Microscopically, the lesion consisted of numerous vascular channels of various size lined by a single layer of flat or plump endothelial cells. Areas of infarction, thrombosis and calcification, and formation of cavernous hemangiomatous foci were also noted in the lesion. Ultrastructurally, the cells had the characteristics of endothelium, including basal lamina, pinocytic vesicles, and Weibel-Palade bodies. Factor VIII-associated antigen was demonstrated in the tumor cells.