A 23-year-old man was admitted to the hospital with hoarseness caused by recurrent nerve palsy. The chest X-ray film and CT scan on admission showed a large mass in the antero-superior part of the mediastinum and a small round mediastinal mass adjacent to right inferior pericardium. Examination of a specimen aspirated from the mediastinal mass revealed thymoma. The tumor was considered to be inoperable because of the pericardial dissemination, and the patient was treated with carboplatin, Adriamycin, and etoposide. After 4 courses of chemotherapy, remarkable regression of both tumors was observed on a chest X-ray film. The patient underwent surgery, and no remaining tumor was found. A combination of carboplatin, Adriamycin, and etoposide may be useful as neoadjuvant chemotherapy for advanced invasive thymoma.