BACKGROUND Testicular germ cell neoplasms occur bilaterally in approximately 2-5% of patients. Bilateral testicular tumors of different histogenesis are extremely rare, and the study of such cases may offer clues to the pathogenesis of both tumor entities. METHODS A report of a case and review of the literature are presented. RESULTS A 33-year-old man had a right-sided testicular neoplasm consisting of teratoma, embryonal carcinoma, and yolk sac tumor. Retroperitoneal lymph node metastases were excised, and, subsequently, adjuvant abdominal radiation therapy was administered. The patient later received six cycles of cisplatin-based chemotherapy for pulmonary relapse. When he was 40 years of age, a contralateral Leydig cell tumor (LCT) was treated by testis-sparing excision. This is the first observation of testicular germ cell tumor (GCT) and contralateral LCT. Three cases of germ cell neoplasm and concurrent ipsilateral LCT have been reported previously. CONCLUSIONS The association of GCT and LCT in one patient is quite unusual because both entities are rare. Sharing of common etiologic factors by both entities is a possible explanation.