Pure RBC aplasia (PRCA) and myasthenia gravis (MG) are occasionally associated with thymoma, although the occurrence of all three in a single patient is rare. We describe a patient in whom PRCA and MG occurred in conjunction with the presence of serum autoantibodies, evidence for a serum inhibitor of erythropoiesis, and elevation of circulating thymosin alpha 1. Although a thymoma could not be detected before death, postmortem examination of the mediastinum found scattered cells within a nodule, suggestive of a lymphoepithelial thymic neoplasm.