Idiopathic intracranial hypertension (IIH) affects roughly 1 to 2 people per 100,000 in the general population each year, making it uncommon but far from rare. The condition, which causes a buildup of pressure around the brain without an obvious cause like a tumor, has been rising sharply in recent decades. Among women of childbearing age, the rates are substantially higher, and in some populations the numbers have climbed dramatically since the 1990s.
Overall Incidence in the General Population
In the United States, the estimated national annual incidence of IIH is about 1.15 per 100,000 people, based on data collected between 1997 and 2016. That number varies meaningfully by country. In Japan, where obesity rates are low, the incidence drops to just 0.03 per 100,000. In Libya, it’s roughly 2.2 per 100,000. A study from Sheffield in the United Kingdom found an incidence of 1.7 per 100,000, while data from Olmsted County, Minnesota showed the rate roughly doubled from 1.0 per 100,000 before 1990 to 2.4 per 100,000 between 2002 and 2014.
These differences map closely onto regional obesity rates. A nationwide U.S. study found that IIH prevalence among women aged 18 to 55 was 3.44 per 10,000, with significant geographic variation across states. States with higher obesity rates consistently showed higher IIH prevalence.
Who Gets IIH Most Often
IIH overwhelmingly affects women. In the U.S., women are roughly eight times more likely to be diagnosed than men. Among women aged 15 to 44, the annual incidence is about 3.5 per 100,000, compared to 0.3 per 100,000 for men in the same age range. In some Middle Eastern populations, the gender gap is narrower, with women about three times more likely to be affected than men.
Body weight is the strongest known risk factor. Nearly all adult patients with IIH are overweight or obese, and the link between higher BMI and IIH is consistent across every population studied. Higher BMI also worsens outcomes: for every 10-unit increase in BMI, the odds of severe vision loss jump by about 1.4 times. At a 20-unit BMI increase, the odds double.
IIH in Children
IIH can also occur in children, though it’s less common. The annual incidence in pediatric populations ranges from 0.6 to 0.9 per 100,000 worldwide. Before puberty, the condition looks quite different from the adult version. Prepubertal children are more likely to be asymptomatic, less likely to be obese, and the gender split is roughly equal between boys and girls. After puberty, the pattern shifts to mirror adult demographics, favoring overweight females.
IIH in Men
While IIH is uncommon in men, the cases that do occur tend to be more serious. Men with IIH are more likely to present with severe vision loss and significant visual field defects compared to women. They’re also more likely to need surgical treatment because the condition is less responsive to standard medication. In one clinical trial, men had 26 times the odds of medical treatment failure compared to women, though the number of male participants was small. The takeaway is that while fewer men develop IIH, those who do face a more aggressive disease course on average.
Rates Are Rising Fast
Perhaps the most striking finding in recent years is how rapidly IIH incidence has increased. A large U.S. database analysis covering 1990 to 2024 found that the adult incidence rose from 16.0 per 100,000 in the 1990s to 127.0 per 100,000 between 2020 and 2024. That’s roughly a sevenfold increase after adjusting for other factors. These numbers are considerably higher than older estimates, likely reflecting both a genuine rise in cases driven by increasing obesity rates and improved awareness and diagnosis.
The adult cohort aged 20 to 64 showed the steepest climb. This trend has prompted calls for public health efforts targeting obesity in young women as a strategy to reduce IIH risk in the highest-risk groups.
Why Numbers Can Be Misleading
IIH is frequently misdiagnosed, which complicates any attempt to pin down exactly how common it is. The condition mimics common headache disorders, and many patients initially receive a diagnosis of chronic migraine or tension headache. In one retrospective study of patients referred with suspected IIH, 72% ultimately turned out not to have it. Their final diagnoses were mostly primary headache disorders (70% of the false cases) and a condition called pseudopapilledema, where the optic nerve appears swollen but isn’t actually under pressure (12%).
Misdiagnosis cuts both ways. About 11% of patients in that study were genuinely misdiagnosed, including nine who were falsely told they had IIH when they didn’t. Diagnosing IIH requires ruling out every other cause of elevated brain pressure, confirming the pressure is truly elevated through a lumbar puncture, and finding characteristic signs on brain imaging. This makes it easy to both over-count and under-count cases depending on how rigorously diagnostic criteria are applied in a given study or healthcare system.
The Bottom Line on Prevalence
For the general population, IIH remains an uncommon condition, with roughly 1 to 2 new cases per 100,000 people annually in most Western countries. For women of childbearing age with obesity, the risk is meaningfully higher. And across all demographics, the condition is becoming more common year over year, closely tracking global trends in body weight. If you’re a young woman experiencing persistent headaches with visual changes, particularly with ringing in the ears or brief episodes of vision going dark, IIH is worth discussing with a doctor, even though most headaches will turn out to have a more common explanation.