A 32-year old man, apparently asymptomatic, was found dead in his apartment. Autopsy revealed a large necrotic mediastinal mass with liver and occipital brain metastases, the latter having produced acute intraparenchymal and intraventricular hemorrhage with cerebellar tonsillar herniation. Histologically, the mediastinal mass and metastases were consistent with immature extragonadal teratoma, with malignant transformation of the intestinal-type epithelium. Undiagnosed neoplasms as causes of sudden death are quite rare and usually reported in older age groups; however, in one study of autopsies in a 25-to 46-year-old age group, a significant 3.2% was reported. Germ cell tumors of the mediastinum are the most common extragonadal primary site, accounting for ∼50%-70% of extragonadal germ cell tumors (EGCTs) and primarily affecting 20- to 35-year-old men. EGCTs are usually symptomatic at the time of diagnosis, although a large proportion may be asymptomatic. This case represents one the few reported cases of sudden death as a result of mediastinal EGCT; it also demonstrates the natural course of this disease and underscores the importance of medicolegal autopsies in cases of sudden death.