Idiopathic intracranial hypertension (IIH) is a condition of unknown etiology, primarily affecting overweight females of childbearing age. Typically, patients experience headache and visual symptoms due to increased intracranial pressure (ICP) and papilledema. The diagnosis is difficult, and outcomes vary from no sequelae to blindness or chronic headaches. No clear prognostic indicators exist. Treatment consists of medication, weight loss, and possibly surgical intervention.There is an unmet need of defining biomarkers with prognostic or diagnostic value and defining predictors of a poor outcome. This project is a prospective, population-based cohort study including clinical data and a biobank (blood samples and cerebrospinal fluid). The investigator's primary aim is to identify biomarkers of diagnostic or prognostic value and to create a clinical IIH database. The clinical database will answer questions about patient characteristics at baseline and during follow-up, identify predictors of outcome, and help create a standardized programme for follow-up and