Extrauterine pelvic hemangiopericytomas are rare tumors with malignant potential. Herein, we report a case of a 55-year-old male who presented with hydronephrosis and obstructive urinary symptoms. Cystoscopy, imaging and biopsy were unable to provide a definitive preoperative diagnosis. He underwent pelvic mass resection, and final pathology revealed malignant hemangiopericytoma. The patient is being closely monitored with serial imaging, and remains disease-free at 23 months of post-operative follow-up without adjuvant therapy. Our experience and evidence from the existing literature suggests that given the rarity of these tumors, adherence to standard oncologic principles is necessary to ensure adequate resection and appropriate follow-up.