In those four cases, we assume that the mechanism contributing to the development of Hashimoto’s thyroiditis is due to expansion of immune response, i.e. an autoimmune process that stimulates the TSH receptor; in this case, TRAb to produce autoantibodies toward thyroid peroxidase (TPO) and thyroglobulin (Tg). We propose such mechanism since in those cases, no examination on TRAb or TSBAb has been conducted at the begining stage of Graves’ disease to confirm concurrence of both diseases.