This was a case of primary choriocarcinoma arising in transitional cell carcinoma of the urinary bladder in a 52 year old male. The choriocarcinoma was associated with a high level of serum human chorionic gonadotropin, and the tumor cells revealed hCG positive granules with peroxidase-anti-peroxidase reaction. The histogenesis of non-gestational choriocarcinoma of the urinary bladder was discussed briefly.