A case of myasthenia gravis (MG) with thymus hyperplasia and pure red cell aplasia (PRCA) is reported. A 57-year-old woman was diagnosed as having MG and was treated with thymectomy 26 years ago. The histology of the resected thymus was thymic lymphoid follicular hyperplasia. She developed rapidly progressive anemia and a bone marrow examination revealed PRCA. Her hematological results improved with oral administration of cyclosporine A. Cases of MG, thymoma and PRCA have been reported in the literature. We report the first case of MG without thymoma and PRCA.