We report a case of a solitary fibrous tumor of prostate presenting with urinary retention and a large prostate mass. We describe the clinical presentation, magnetic resonance imaging findings, and histopathology of this rare, benign tumor. Although clinical and radiologic appearances embrace various differential diagnoses including sarcoma, this mass was confirmed by histologic analysis following surgical resection. We report this rare, benign tumor to help the radiologist suggest the diagnosis when presented with a similar case.