A small number of patients with hyperthyroidism who are ineffective after iodine-131 treatment or who are in partial remission need to undergo iodine-131 treatment again. In other cases, because the triggering factors for hyperthyroidism persist (or new causes appear), the condition remits and then relapses (or even reappears after a period of hypothyroidism), which requires repeat Iodine-131 treatment. The interval between repeated iodine-131 treatment and the first treatment is usually at least three months. The methods, precautions and follow-ups for repeat Iodine-131 treatment are basically the same as for the first Iodine-131 treatment (the specific decision is made by the doctor in charge of the treatment according to the specific condition), except that the probability of future hypothyroidism due to repeat treatment is increased, so the time for follow-up visits to the hospital after repeat Iodine-131 treatment should be appropriately shortened and the frequency of examinations should be appropriately increased. Only very few patients need a third or even more iodine-131 treatment.