Although a lack of dietary iodine is the main cause of goiter in many parts of the world, this is not often the case in countries where iodine is routinely added to table salt and other foods. 1  Graves' disease. 2  Goiter can sometimes occur when your thyroid gland produces too much thyroid hormone (hyperthyroidism). Goiter can sometimes occur when your thyroid gland produces too much thyroid hormone (hyperthyroidism). 2  In Graves' disease, antibodies produced by your immune system mistakenly attack your thyroid gland, causing it to produce excess thyroxine.