The clinical courses of 60 patients with hemangiopericytoma of the somatic soft tissues are summarized in this retrospective study. The tumors were subjected to a comparative histologic review and classified as benign (12 lesions), borderline malignant (16 lesions), and malignant (32 lesions). Tumors with 1 mitotic figure per 10 high-power field and moderate cellular anaplasia or 1 mitotic figure per 20 high-power fields and moderate cellular anaplasia may be expected to follow a malignant clinical course. Six of the 16 tumors with these microscopic features (borederline lesions) metastasized (37.5%), and 6 exhibited local recurrences after excision. Of the 32 malignant tumors, 25 (78%) metastasized. Twenty-three patients with malignant tumors were followed for more than 5 years or until death from tumor, and only one patient was alive and free of disease. Fifteen of the 23 patients experienced one of more local recurrences. None of the benign tumors metastasized. Surgical ablation of hemangiopericytioma is, in our experience, the only satisfactory method of treatment. Amputation of an extremity need be done only when the location of the lesion precludes a wide local excision. Local recurrent tumor was experienced by 22 patients after an inadequate local excision. Long-term follow-up is recommended because metastasis became apparent in 11% of patients with malignant tumors and 7% with borderline tumors after 5 "disease-free" years.