The thyroid gland is located at the base of the neck, in front of the trachea (windpipe) and esophagus (tube that connects the mouth with the stomach). The thyroid produces thyroid hormone, which helps regulate many body functions. In hyperthyroidism, the thyroid is overactive and produces more thyroid hormone than the body needs. Women are more likely than men to have hyperthyroidism, and it affects younger persons more than elderly persons. This Patient Page is based on one published in the July 6, 2005, issue of JAMA.