The patient was a 21-year-old man with a shadow on a chest roentgenogram taken during a medical checkup. According to blood testing, thoracoabdominal computed tomography, head magnetic resonance imaging, and lung tumor biopsy, we diagnosed a primary retroperitoneal germ cell tumor with multiple lung and brain metastases. Induction chemotherapy (4 courses of Bleomycin, Etoposide and Cisplatin) was started immediately. Because tumor markers remained elevated, salvage chemotherapy (4 courses of paclitaxel, ifosfamide cisplatin) was administered. Since the tumor markers remained elevated third-line chemotherapy was considered. However, because the tumor markers continued to decrease gradually and the tumor continued to shrink on imaging, expectant management was given. Three months later, the tumor markers turned negative, and retroperitoneal lymph node dissection and resection of lung metastases were performed. No cancer cells were found in any of the tissue samples. Careful monitoring after completion of chemotherapy may spare unnecessary chemotherapy.