A 71-year-old man underwent extended thymomectomy with partial resection of the upper lobe of the left lung and pericardium for stage III invasive thymoma in March, 2000. Postoperative chemotherapy and radiation therapy were carried out. The patient did well until June 2005, when a mediastinal mass and pleural dissemination were detected. The recurrence of the thymoma was strongly suspected radiographically. Combination chemotherapy of carboplatin and paclitaxel achieved partial remission. About three months after the last chemotherapy, the patient had a severe anemia in February 2006. Based on the blood data and the bone marrow examination, pure red cell aplasia was diagnosed. Prednisolone treatment (50 mg daily) resulted in dramatic regression of recurrent mediastinal and pleural tumors, as well as improvement of pure red cell aplasia.