Among 417 patients treated with cisplatin-based chemotherapy for germ cell malignancy (median follow-up 7 years) we observed 6 patients who developed a second tumor of the testis. In 3 cases the first tumor was of testicular origin, whereas in the other cases the initial tumor presented in the retroperitoneal space. Although cisplatin-based chemotherapy may reduce or delay the development of a contralateral testicular tumor, the risk apparently is not completely eliminated. Patients with primary retroperitoneal germ cell tumors need a close and careful follow-up, as they appear to be at an increased risk for developing a testicular tumor.