Adult extrarenal nephroblastomas (Wilms' tumor) are extremely rare tumors. They show a higher incidence of non-seminomatous elements and these so-called 'teratoid' Wilms' tumors are suggested to be of germ cell origin. To date, however, the number of reported cases with gonadal teratoma containing nephroblastoma is very low, and due to this reason, there are no standardized criteria for the categorization and treatment of these lesions. To our knowledge, the first case of nephroblastoma arising in a non-atrophic testis has been reported and it is associated with a teratoma as morphologically identifiable germ cell tumor and rhabdomyosarcoma as a second non-germ cell element. We report the second case of an adult nephroblastoma that arose within the primary testicular teratoma in a non-atrophic testis. Teratoma and nephroblastoma within the same testis may have an important point to clarify the developmental mechanism in nephroblastomatous differentiation of germ cell tumors.