In the genitourinary tract, masses in the seminal vesicles, particularly primary tumors, are an unusual event. One must consider all diagnoses including Ewing's sarcoma or its variant, peripheral primitive neuroectodermal tumor (PPNET). In this case report we describe a case of PPNET arising from the seminal vesicle. The prognosis of such tumors is generally poor and requires aggressive multimodal management if it is to be successful. It is essential that unusual tumors are considered when confronted by a seminal vesicle mass and that appropriate investigation and management are initiated.