Idiopathic hypersomnia has long been considered a rare disease, believed to be 10 times less frequent than narcolepsy.[9] The prevalence of narcolepsy (with cataplexy) is estimated between 1/3,300 and 1/5,000.[45] Although the true prevalence of idiopathic hypersomnia is unknown, it is estimated at 1/10,000 – 1/25,000 for the long sleep form and 1/11,000 to 1/100,000 without long sleep.[46] A more precise estimate "is complicated by a lack of clear biologic markers" and a lack of "unambiguous diagnostic criteria."[47]