A 31-year-old man came to our hospital with chest pain and was diagnosed to have a left testicular tumor with metastasis to the lung, and cervical, mediastinal, and retroperitoneal lymph nodes. Left orchiectomy was performed, and histological diagnosis was seminoma. Serum tumor markers were normalized after 3rd-line chemotherapy, but lymph node metastases were still enlarged. Then the cervical lymph node was excised, and histologically diagnosed as mature teratoma. Based on these results, we diagnosed this case as growing teratoma syndrome. Since the whole metastasis was too large to be completely excised, we started systemic interferon alfa-2b (IntronR A) administration. The metastasis initially responded to the therapy by 20% reduction in size and remained stable thereafter. However, the mediastinal lesion caused obstructive pneumonia, which was bronchoscopically resected. At the time of 12 years after the initial presentation, the tumors are well controlled with stable disease or only modest increase.