Testicular germ cell tumor in patient with Klinefelter syndrome.

Although mediastinal germ cell tumors are known to occur with a greater frequency in patients with Klinefelter syndrome, reports of testicular germ cell tumors occurring in such patients are rare. We report a case of a nonseminomatous germ cell tumor in a patient with Klinefelter syndrome and suggest that such an association may occur more frequently than has been reported previously.