Although iodine-131 has many advantages in the treatment of hyperthyroidism, it also has some limitations. Therefore, iodine-131 should be used with caution or not in the following cases: (1) Pregnant women or women with hyperthyroidism who are breastfeeding; Lu Hankui, Department of Nuclear Medicine, Shanghai Sixth People’s Hospital; (2) Patients who fear lifelong hypothyroidism. (3) Severe thyroid proptosis (invasive proptosis) in the active phase. (4) Iodine uptake rate is too low or the cause of hyperthyroidism is still unclear. (5) Combined thyroid nodules in an enlarged thyroid gland that are compressing critical areas such as the trachea and esophagus.