Increased secretion of thyroid hormones is called hyperthyroidism. One of the causes for hyperthyroidism is Graves's disease wherein the thyroid stimulating autoantibodies produced by B-lymphocytes activate the TSH receptors and increase the secretion of thyroid hormones. Intolerance to heat is a common symptom in hyperthyroidism. Increased sweating occurs due to vasodilation. Hyperthyroidism causes edematous swelling of the retro-orbital tissues and degenerative changes in the extraocular muscles leading to protrusion of the eyeball. There is almost total absence of TRH and TSH in serum. Treatment of hyperthyroidism involves medical management, radiotherapy and surgical intervention.