Purpose To re-evaluate the population-based incidence of idiopathic intracranial hypertension (IIH) and to determine if it mirrors the rise in obesity. Design Retrospective, population-based cohort. Participants All residents of Olmsted County, Minnesota, diagnosed with IIH between January 1, 1990, and December 31, 2014. Methods All cases of IIH were identified using the Rochester Epidemiology Project, which is a record-linkage system of medical records for all patient–physician encounters among Olmsted County, Minnesota, residents. All medical records were reviewed to confirm a diagnosis of IIH. The incidence rates of IIH were compared against the incidence of obesity in Minnesota over the same period. Main Outcome Measures Incidence of IIH, lumbar puncture opening pressures, and body mass index. Results There were 63 new cases of IIH, yielding an overall age- and gender-adjusted annual incidence of 1.8 per 100 000 (95% confidence interval, 1.3–2.2) between 1990 and 2014. It increased from 1.0 per 100 000 (1990–2001) to 2.4 per 100 000 (2002–2014; P = 0.007). The incidence of IIH was 3.3 per 100 000 in women and 0.3 per 100 000 in men (P ≤ 0.001). In obese women 15 to 44 years of age, the incidence was 22.0 per 100 000 compared with 6.8 per 100 000 among all women in the same age group. A strong correlation was observed between IIH incidence rates and obesity rates in Minnesota (R2 = 0.70, P = 0.008). Conclusions The incidence of IIH has increased since 1990, which is highly correlated with the rise in obesity during the same period.