The case of a 26 years old patient with a primary paraaortic extragonadal yolk sac tumor is presented. After operative reduction of the tumor polychemotherapy with PEB was performed. Following chemotherapy testicular biopsy did not show histological changes typical for testicular intraepithelial neoplasia (TIN). Three years after the initial manifestation of the yolk sac tumor, a malignant tumor of the testis with components of undifferentiated teratoma and yolk sac tumor was observed. In this paper the problems of development of testicular malignancy after polychemotherapy and the validity of a small exploratory excision of testicular tissue in retroperitoneal germ cell tumors and following chemotherapy are discussed.