Included in this study are 513 patients with Graves' disease who underwent thyroidectomy between 1970 and 1983. The patients were divided into three groups by dividing the period in which the surgical procedures were done. The weight of the remnant of the thyroid gland and the incidence of surgical complications were collated for the patients in each group studied. Postoperative function of the thyroid gland was evaluated clinically and biochemically and compared with the remnant weight and total weight of the thyroid gland. The remnant weight was greatest in the first period and least in the third period. There were no differences between the frequencies of postoperative complications among the three groups in site of a remarkable decrease of the remnant weight in the third period. Remission of hyperthyroidism, including those with a latent hypothyroid state, was most frequently observed in the group in which the remnant weight was from 4 to less than 8 grams. These results indicate that the remnant weight appears to be one of the most crucial factors influencing the postoperative outcome; it thus seems appropriate to leave only small remnants of the thyroid gland (4 to less than 8 grams) at thyroidectomy. In our hands, surgical treatment is an effective and safe procedure for Graves' disease, although the precise mechanism for the remission induced by this procedure has not been elucidated.