We describe a rare case of autoimmune polyglandular syndrome type 2 initially presenting as Addison disease and autoimmune thyroid disease, with subsequent development of autoimmune hepatitis and myasthenia gravis (MG) crisis in a Japanese woman. MG improved with oral prednisolone followed by plasmapheresis for immunoadsorption; thymectomy was not performed. Conventional treatment for MG was effective and safe in this case, in which there was positivity for human leukocyte antigen A23, B52, B62, DR11, and DR15.