The population-based incidence rates and clinical features of idiopathic intracranial hypertension (IIH) are reported from the Mayo Clinic. Nine patients (8 women, 1 man) were identified among Rochester residents over a 15-year period (1976-1990). The mean age at diagnosis was 28 years (range, 15-40). The annual age-adjusted rates per 100,000 were 0.9 for the total and 1.6 for females. The ratio of female-male age-adjusted rates was 8.4:1.0. For women, the annual incidence rates per 100,000 were 3.3 for the total and 7.7 for those with obesity. Headache was present in all but one and papilledema in all patients when first examined. Mild visual impairment developed in 3 of 18 eyes during a median follow-up of 2.7 years. Visual fields and acuity were normal in 7 of 8 females. 
COMMENT. Diagnosis of IIH requires the following criteria: IH, normal neuro exam except papilledema and VI nerve paresis, no ventricular enlargement or tumor, normal CSF composition. Frequently reported severe deficits in visual acuity were absent in the present series. Early diagnosis and therapy were cited as the probable explanation for the sanguine prognosis. The absence of pediatric cases was surprising. A review of the literature on “benign intracranial hypertension” showed that 84 (37%) of 224 patients were children; 75 children (90%) were between 5 and 15 years.