The first reported cases of preoperatively embolized hemangiopericytomas are presented. Both lesions presented in the retroperitoneum where most lesions are now considered to be malignant. In the past, the highly vascular nature of these tumors has made resection in these areas difficult. Since the angiographic picture of hemangiopericytomas is now thought to be specific, it became feasible to add preoperative embolization to the overall management of these cases. In the first case, the diagnosis had been established 15 years previously. When first seen at Thomas Jefferson University Hospital, extensive bone destruction of the sacrum and lumbar vertebrae were present. Preoperative Gelfoam embolization aided in the palliative debulking of the tumor at operation. With this experience, preoperative embolization became part of the management in the second case and aided in the complete surgical removal of the tumor. Radiation therapy in the dosage of 5000 rad was given postoperatively in this case and should also be part of the treatment plan for these lesions.