A case of retrovesical leiomyosarcoma in a male patient is described. The preoperative radiological and laboratory studies were inconclusive in determining the primary origin of the tumor. Diagnosis of a malignant tumor with smooth muscle origin was suggested by needle biopsy. However, the definitive diagnosis and the primary site of origin could only be determined by surgical exploration and subsequent histopathologic examination after excision. No sign of recurrence or metastasis was present 12 months after complete surgical resection.