We report a 40-year-old woman with recurrent thymoma associated with myasthenia gravis, in whom an unusual form of erythroderma developed. A histological examination revealed a graft-versus-host disease (GVHD)-like reaction. After high-dose steroid therapy, the metastatic thymoma lesion in the abdominal cavity was reduced in size from 9.5 x 6 x 7.5 cm to 4 x 3 x 1 cm in diameter. Nevertheless, the GVHD-like erythroderma become aggravated, her condition worsened, and the patient finally suffered from respiratory failure and died of sepsis. A GVHD-like reaction may be a rare presentation of thymoma-associated immunological disorders such as myasthenia gravis or pure red cell aplasia. Herein, we discuss the present case and review pertinent reports of thymoma cases associated with GVHD.