When treating hyperthyroidism with I-131, patients are usually faced with a choice: whether to have multiple small doses or a single high dose treatment. It is well known that an important complication after I-131 treatment is hypothyroidism. Many physicians have gone to great lengths to reduce this complication. From the derivation of various dose formulas, to the study of various risk factors, to multiple small dose attempts at treatment, and so on, the hope is that the dose of I-131 will be just right for controlling hyperthyroidism without hypothyroidism. However, the results are often unsatisfactory. One of the most common causes of hyperthyroidism in outpatient clinics is Graves’ disease and the other is Hashimoto’s hyperthyroidism. Hashimoto’s hyperthyroidism is the most common cause of hypothyroidism and has a high probability of occurring with either medication or I-131 therapy, except that I-131 therapy causes hypothyroidism to appear earlier and more directly. I-131 therapy for Graves’ disease does result in some patients being cured of hyperthyroidism without hypothyroidism, but this is a very complex issue that is difficult to apply to every patient. For the physician, hypothyroidism is not a scary problem; it is the recurrence of hyperthyroidism that needs to be actively prevented. To be clear, some patients with Graves’ disease can temporarily obtain normal nail function after low-dose I-131 therapy, but the risk of long-term relapse is very high. The final choice of which method to use is ultimately a matter of consultation between the patient and the receiving physician. However, the high-dose method is recommended in the following cases: 1) huge thyroid gland with obvious hyperthyroidism; 2) combined with other diseases such as heart failure, hyperthyroidism crisis, diabetes, renal insufficiency, malignancy, etc.; 3) those who need artificial pregnancy assistance; 4) combined with thyroid nodules; 5) patients with high-functioning adenoma; 6) ectopic thyroid gland or ectopic endocrine.