Five cases of pelvic hemangiopericytomas are reported. One of these tumors arose from the uterus, and four patients had extrauterine, pelvic hemangiopericytomas. The patient with a primary uterine hemangiopericytomas had only simple excision, and, after 6 years, is alive and free of disease. All four patients with extrauterine, pelvic hemangiopericytomas had incomplete resection of their tumors because of hemorrhage. However, pelvic radiation therapy was then employed in these patients and produced a complete regression in one patient and partial regression in two patients with minimal shrinkage in another patient. The latter patients were reexplored after pelvic radiation and underwent complete resection of their disease. Two patients developed pelvic recurrences at 2 and 9 years, respectively, and these were effectively resected. All four patients are all alive and free of disease 5 to 18 years later. If this lesion is unexpectedly discovered at laparotomy, our experience suggests that the resection should be discontinued and that they should be treated with pelvic radiation and delayed resection of persistent and recurrent pelvic tumors.