Patients with testicular germ cell tumors who have disease-free remission for more than 2 years are usually considered to be cured of their disease. This report describes a case of a germ cell tumor recurring 12 years after initial diagnosis and its treatment in a 35-year-old man who developed a retroperitoneal mass adhering to the abdominal aorta with a bout of severe colic in the left flank. Although tumor markers were not elevated and histology of the biopsy specimen was initially diagnosed as adenocarcinoma, we finally concluded that the retroperitoneal tumor was teratoma developing as a recurrence of the germ cell tumor for the following reasons: (1) the histology of the specimen was similar to an epithelial component of teratoma found in the tissue resected 12 years before; (2) systemic survey failed to detect any other primary site; (3) the young age of this patient was consistent with germ cell tumor rather than adenocarcinoma; and (4) the retroperitoneum is the most frequent site of late recurrences of testicular cancer. He was treated successfully with combination chemotherapy of cisplatin, etoposide and bleomycin followed by surgery. It is important to differentiate this treatable disease from metastasis from an unknown primary, because the latter responds poorly to therapy and survival is usually short.