Hydrocephalus is uncommon but far from extremely rare. Over one million people in the United States are currently living with it, and congenital hydrocephalus occurs in roughly 2 to 18 out of every 10,000 live births worldwide. The condition also develops later in life after brain injuries, infections, or bleeding events, and it becomes surprisingly common in people over 80.
How Common Is It at Birth?
Congenital hydrocephalus, where excess cerebrospinal fluid builds up in and around the brain before or shortly after birth, varies significantly by region. In California, the rate is about 6 per 10,000 live births. In Saudi Arabia it’s roughly 16 per 10,000, and in parts of Egypt rates reach nearly 68 per 10,000. Denmark has one of the lowest recorded rates at just 0.6 per 10,000 births.
These wide gaps reflect differences in prenatal care, nutrition, infection exposure, and how aggressively screening programs catch cases. In low- and middle-income countries, post-infectious hydrocephalus is a major driver. In one South African study, infections caused about a third of all pediatric hydrocephalus cases, with tuberculous meningitis responsible for more than half of those.
Premature infants face elevated risk. When preterm babies develop severe bleeding in the brain (grade III or IV intraventricular hemorrhage), roughly one in four goes on to develop hydrocephalus. By comparison, only 1 to 4 percent of babies with milder bleeding develop the condition.
Genetic Causes Are Genuinely Rare
A small fraction of congenital cases trace to inherited genetic mutations. The most well-known is a mutation in the L1CAM gene, which causes an X-linked form of hydrocephalus passed from mothers to sons. Over 300 disease-causing variants of this gene have been cataloged, but the condition itself remains uncommon. Most congenital hydrocephalus has no clear genetic cause and instead results from developmental abnormalities, infections during pregnancy, or complications of prematurity.
Hydrocephalus in Older Adults
Normal pressure hydrocephalus (NPH) is a distinct form that develops in older adults. The ventricles in the brain gradually enlarge with fluid, but pressure readings on a spinal tap can appear normal, which makes it tricky to diagnose. NPH causes a recognizable triad of symptoms: difficulty walking, cognitive decline, and bladder control problems.
Prevalence rises steeply with age. Among people in their 70s, roughly 0.2% meet the diagnostic criteria. By age 80 and beyond, that figure jumps to nearly 6%, making it far more common than most people realize. A Japanese community study found rates of about 3% in people over 65, while European surveys have reported lower figures between 0.1% and 0.4% in the same age range. These differences likely reflect both genetics and how carefully populations are screened.
An estimated 80% of people with NPH are never correctly diagnosed. Most are told they have Alzheimer’s disease or Parkinson’s disease instead. This matters enormously because NPH is one of the few causes of dementia-like symptoms that can actually be treated. A surgically placed shunt to drain excess fluid often improves or reverses symptoms, especially walking difficulties.
Hydrocephalus After Brain Injuries
Hydrocephalus can also develop after a traumatic brain injury, a stroke, or a brain hemorrhage. Among people with severe traumatic brain injuries, about 2% develop hydrocephalus within the first three months. Even people with less severe injuries carry some risk, with about 0.5% developing the condition. The fluid pathways in the brain become blocked or scarred by the original injury, and fluid gradually accumulates.
How Many People Are Affected Overall?
The Hydrocephalus Association estimates that more than one million Americans are living with some form of the condition. That includes children born with it, adults who developed it after an injury or illness, and older adults with NPH. In the pediatric population alone, about 20,000 shunt surgeries are performed each year in the United States. Roughly 44% of those are revision surgeries, since shunts frequently malfunction or become outgrown, requiring repeated operations over a person’s lifetime.
To put the numbers in perspective, hydrocephalus is less common than epilepsy (which affects about 1 in 26 people) but more common than conditions like ALS or Huntington’s disease. It sits in a middle range where it’s uncommon enough that most people have never heard of it, yet widespread enough that every neurosurgical center treats it regularly. The combination of congenital cases, post-injury cases, and the large pool of undiagnosed older adults with NPH means the true burden is almost certainly higher than official estimates suggest.