Swelling of the neck after iodine 131 is usually not a good thing, indicating that radiation thyroiditis may have occurred. Radioactive thyroiditis is a complication of iodine 131 treatment, caused by ionizing radiation leading to different degrees of inflammatory changes in the thyroid gland, often occurring within 7 to 10 days after iodine 131 treatment, the clinical manifestations of discomfort in the neck, a feeling of pressure, skin edema on the surface of the neck, itching and so on. At this time, immediately removed from the source of radiation can generally be relieved within a few days, the symptoms of serious cases can be treated with aspirin, prednisone and other drugs. Iodine 131 treatment neck swelling, it is recommended to go to the hospital in a timely manner, under the guidance of the doctor to determine the cause of the disease and timely treatment, so as not to delay the condition.