Goiter is an enlargement of the thyroid gland in the neck, causing swelling below the larynx. It may represent the smooth swelling of an overactive gland in thyrotoxicosis or more often the enlargement caused by multiple cysts and nodules without functional change.

Endemic goiter is enlargement associated with iodine deficiency, occurring in certain areas where the element is lacking in the soil and water. Rarely, goiter is due to thyroid cancer. If there is excessive secretion or pressure on vital structures surgery may be needed, although drug treatment or radiotherapy for excess secretion are often adequate.