The clinicopathologic and the flow cytometric DNA characteristics of 14 patients with sinonasal hemangiopericytomas are presented. Patient and tumor characteristics were similar to previously published series. Flow cytometric analysis revealed a diploid DNA pattern and low S-phase in 13 neoplasmas and an aneuploid DNA pattern with relatively high S-phase in one. Histopathologically, all diploid and low S-phase neoplasms displayed relatively uniform cellular features and low mitotic counts. All patients are alive and free of disease; one is still alive after a single recurrence. Our data suggest that sinonasal hemangiopericytomas are low-grade neoplasms as evidenced by their histomorphology and their DNA content. Recurrences are delayed and can be controlled.