We describe the clinical and pathologic findings of a young man with a heterogeneous mediastinal tumor metastatic to both lungs, and containing a predominant pattern of classic biphasic pulmonary blastoma with elements of immature teratoma, seminoma, and embryonal carcinoma. Beta-human chorionic gonadotropin and alpha-fetoprotein were elevated at presentation and responded to four cycles of bleomycin, etoposide, and cisplatin although the tumor did not regress. The patient ultimately progressed through paclitaxel, ifosfamide, and cisplatin and tandem autologous bone marrow transplants. Classic biphasic pulmonary blastoma is a rare tumor of young adults. Surgery is the primary treatment, but prognosis is poor and chemotherapy and radiation have been used for unresectable disease. A discussion of pulmonary blastoma and extragonadal germ cell tumors is presented.