This study documents for the first time the extraordinary costs to take care of patients with a chronic, non-fatal, relatively rare disorder who have been incorrectly thought to have an insignificant and self-limiting illness. Idiopathic intracranial hypertension (IIH) occurs worldwide and in all racial groups and is found predominantly in obese women (∼90%) of childbearing age. Although the incidence of IIH is increasing as a result of the rapid increase in obesity, the disorder in general receives little recognition, and no recognition of the extensive burden of healthcare costs placed on patients, their families and society. We established for the first time both the prevalence of IIH in the USA and the direct and indirect costs of IIH using a prevalence-based model. IIH patients had an exceptionally high hospital admission rate of 38% (in 2007), a partial reflection of unsatisfactory treatment options. The total hospital costs per IIH admission in 2007 were four times greater than for a population-based per person admission. Total economic costs of IIH patients exceeded $444 million. Programmes designed to reduce obesity prior to and after diagnosis and better therapeutics will have a tremendous economic impact.