The response of hemangiopericytoma to radiation therapy was studied in 11 patients treated at Memorial Hospital. Response of greater or lesser degree was noted in 26 of 29 radiation therapy courses administered. These included 14 instances of complete tumor regression. Dose and tumor size were the main factors influencing response. The tumors tend to regress slowly and incompletely; yet effective relief of symptoms and long term local control (average duration 27 months) usually was achieved. These results and those reported by others believe the alleged inefficacy of radiation therapy in the management of these tumors. Palliative radiation therapy seems to be worthwhile even in advanced cases. Because of the high rate of local recurrence after surgical excision, treatment strategies combining local excision of large primary tumors with wide-field, high-dose radiation therapy are worthy of trial.