A 27-year-old Japanese male presented with gross hematuria and right frank pain, and was diagnosed of having a right ureteral stone by IVP. Though the stone was passed spontaneosuly, gross hematuria continued, and his urinary stream became week. The prostate was moderately enlarged. The prostate biopsy was initially thought to represent prostate rabdomyosarcoma. He underwent a pelvic extenteration followed by chemotherapy with dacarbazing and ADM. Three years after the pelvic exenteration, coin lesions were found on a chest X-ray film. He was diagnosed as embryonal cell carcinoma of the left testis with pulmonary metastasis and received 3 courses of PVB therapy. At this time, the former diagnosis of prostatic rabdomyosarcoma was changed to prostatic rabdomyosarcoma was changed to prostatic seminoma, because placental-ALP staining was positive. This patient had two distinct germinal cell tumors in the prostate and the left testis. He was alive without any tumor recurrence 20 months after PVB chemotherapy. To the best of our knowledge our report represents the first patient of seminoma of the prostate in the world.