Graves' disease is the most common cause of hyperthyroidism in the United States, affecting 30 per 100,000 people annually. It is caused by antibodies that stimulate the thyroid gland to overproduce hormones, which can lead to a variety of symptoms including anxiety, irritability, rapid heartbeat, and eye problems. While Graves' disease is usually easily diagnosed by its symptoms and physical signs, in some cases further testing is required. If left untreated, it can cause severe thyrotoxicosis and even be fatal, but treatment with radioactive iodine or medications can effectively control the condition in most patients.