Rathke's Cleft Cyst (RCC), which is located at the intrasellar region, is considered to be the distended remnants of Rathke's pouch, an invagination of the stomodeum. Lined with columnar or cuboidal epithelium of ectodermal origin, RCC usually contains mucoid material and it is found in 13-22% of normal pituitary glands. The cyst rarely leads to the development of symptoms but, when it does, the most common presenting symptoms are headache, visual impairment, hypopituitarism and hypothalamic dysfunction. However, in some cases it presents symptoms of diabetes insipidus, decreased libido and impotence. Recently we experienced a case of RCC inflammation presenting with diabetes insipidus and treated with transsphenoidal surgery. To our knowledge, this is the first report of RCC presenting with symptoms of diabetes insipidus in Korea.