A non-toxic goiter is a diffuse or nodular goiter without hyperthyroidism and is a common clinical thyroid disorder. Patients with untreated non-toxic goiter may develop hypothyroidism or hyperthyroidism as the disease progresses. Iodine-131 treatment for non-toxic goiter is simple, safe, and effective. It can significantly shrink the thyroid gland, has a low recurrence rate, and can be repeated. The disadvantage is that patients may develop hypothyroidism. Indications: Non-toxic goiter with significant enlargement of the thyroid gland, poor results with medication, contraindications to surgery, or refusal of surgery, or recurrence after surgery. Patients with non-toxic goiter who require iodine-131 treatment for cosmetic purposes. Contraindications: Pregnant and lactating patients, those suspected of having malignant thyroid lesions. Treatment: Patient preparation and calculation of the iodine-131 dose before treatment is done in the same way as for iodine-131 for hyperthyroidism Graves’ disease. The planned dose of iodine-131 per gram of thyroid tissue is 2.96-4.44 MBq (80-120 uCi), increasing or decreasing as appropriate depending on the patient’s specific case. Patients with nodular goiter should require a larger dose of iodine-131, which should generally be greater than 3.7 MBq/g thyroid (100 uCi/g thyroid). The degree of thyroid volume reduction is related to the size of the iodine-131 dose. The treatment can be repeated after six months if the condition requires it. Patients who develop hypothyroidism after iodine-131 treatment need to be given thyroxine replacement therapy.