A 25-year-old man was admitted to our hospital because of hemosputum and abnormal shadows on chest X-ray film. The chest film showed a mass shadow located in the right hilum and multiple coin lesions in bilateral lung fields. The chest CT scan showed a bulky mass sized 7 cm X 6 cm at the anterior mediastinum. This case was suspected to be choriocarcinoma because he was young, it was rapidly progressive and also because serum LDH and beta-HCG values were raised. The specimens obtained by surgical biopsy showed HCG-stain positive syncytiotrophoblasts. Cancer chemotherapy was started with CDDP and other anti-cancer drugs, but he succumbed about 3 months after admission. Autopsy findings showed no scar formation of his testes, and the primary lesion was finally diagnosed to be in the anterior mediastinum. Extra-gonadal choriocarcinoma is rare, and beta-HCG is very useful for its diagnosis and the follow-up of the clinical course.