Generally refers to any abnormal enlargement of the thyroid gland. The most common type of goiter, the simple goiter, is caused by a deficiency of iodine in the diet. In an attempt to compensate for this deficiency, the thyroid gland enlarges and may become the size of a large softball in the neck. The general availability of table salt to which potassium iodide has been added ("iodized" salt) has greatly reduced the incidence of simple goiter in many parts of the world. A more serious form of goiter, toxic goiter, is associated with hyperthyroidism. The etiology of this condition is not well understood. A third form of goiter occurs primarily in women and is believed to be caused by changes in hormone production.