Patients with a germ cell tumor (GCT) in one testicle are prone to develop cancer in the contralateral testicle. Metachronous development of a GCT in the remaining testicle occurs in 3% of patients. The synchronous development of bilateral GCT occurs in 0.5% of patients. Bilateral testicular neoplasms are almost always identical histologically. Only five cases of synchronous bilateral GCT of different histologic types have been reported in the literature. The authors report the sixth case of this uncommon phenomenon and discuss its clinical and pathogenetic implications.