Two hundreds and sixteen patients with Graves' disease who underwent subtotal thyroidectomy at Ito Hospital during 1983 and 1984 were studied in order to known about the relationship between the prognosis and preoperative values of TRAb. There were 65 euthyroid patients (30.1%), 112 hypothyroid (51.8%), and 39 hyperthyroid (18.1%). No relationship between postoperative thyroid function and preoperative values of TRAb was observed. Postoperative values of TRAb were significantly higher in hyperthyroid group than in euthyroid group and hypothyroid group at any period. Postoperative values of TRAb were negative in about 90% of the patients of euthyroid group. On the other hand, negative postoperative values of TRAb were also observed in about 40% patients of hyperthyroid group. It is concluded that postoperative thyroid function could not be estimated from preoperative values of TRAb and much care is thought to be necessary to estimate the prognosis from postoperative values of TRAb.