After castration of 2 male Japanese Black calves, hemangiopericytomas developed in the subcutis near the scrotum. Their pericytic origin was demonstrated by the absence of focal densities, positive immunoreactivity for alpha smooth muscle actin, and absent staining for desmin. A similar neoplasm has been reported in a castrated male Japanese Black calf. It is considered that hemangiopericytomas in calves may be closely related to castration and certain bovine breeds.