his paper reports that ninety patients treated with 288 to 2471 MBq of lodine-131 singular dasefor large toxic diffuse goiter. Follow up result shows that thirty-two patients are cure、two make hy-pothyroidism and five-one are of no effect. Gross effective rate is over 92%. Our experierce in thisseries juetifies : it is well-marked and safe that radioiodine reduce size of thyroid. The therapy methodis worthy to be cosidered for the patient with large toxic diffuse goiter of recurrence following oper-ation and instatisfactory past antithyroid drug.