Good's syndrome is an acquired immunodeficiency state associated with thymoma. It is characterized by recurrent infection, autoimmune disease, and immunologic abnormality. The insufficient immunity can be managed by intravenous immunoglobulin (IVIG) replacement therapy. We describe 2 patients who presented with Pneumocystis jiroveci pneumonia and Cytomegalovirus pneumonia after thymectomy for a thymoma. Immunologic study revealed hypogammaglobulinemia with very low B-cell count, consistent with Good's syndrome. They were successfully treated with trimethoprim/sulfamethoxazole and gancyclovir respectively, and they are all well without additional infections, receiving regular IVIG replacement.