We present a case of an immature teratoma of the liver and the mediastinum. A 21-year-old female patient presented with dyspnea, abdominal pain, and abdominal mass. Abdominal ultrasonography showed a liver tumor which is located in the right lobe and composed of cystic and solid elements. Computed tomography (CT) also showed a big mass which contained multiple high density, nodular, semi-solid, heterogenic structures in the liver and another mass which contained multiple low density cystic lesions in the anterior mediastinum. Right thoraco-abdominal approach was performed on the patient and a complete macroscopic resection of tumors was achieved without complications. Both tumours were evaluated as having an intact capsule. The mediastinal tumour extended to the diaphragm on the right side, and is dissected from the 'surrounding lung, pericardium' and excised from diaphragm. Right hepatic lobectomy was performed for liver tumour. Intraoperative frozen sections of the liver tumor revealed teratoma. But the final pathological diagnosis was immature teratoma. Chemotherapy was given after surgery. The patient tolerated the procedure well and her postoperative course was unremarkable. At the first follow up 4 months after surgery she was alive and well and there was no evidence of recurrence, but the patient died within seven months with hepatic recurrence and spreading metastasis.