Mediastinal nonseminomatous germ cell tumor (NSGCT) is rare. NSGCT shows excellent response to cisplatin-based chemotherapy. However, some tumors continue to enlarge despite normal tumor markers after chemotherapy, a rare condition called growing teratoma syndrome (GTS). Recognition of this condition is imperative for prompt surgical resection to prevent further cardiopulmonary compression and to improve survival. Multidisciplinary team meeting is important for perioperative preparation and care to improve the outcome of this high-risk surgery. Here, we report two cases of mediastinal GTS and underwent surgical resection, of which one died of pericardial decompression syndrome and the other is well.