The answer depends on how you define the term. Estimates range from about 0.018% to 1.7% of the population, a nearly 100-fold difference that comes down to which conditions get counted. The word “hermaphrodite” is outdated in medicine and considered inaccurate for humans. The current medical term is intersex, or more formally, differences of sex development (DSD). These are congenital conditions where a person’s chromosomes, hormones, or anatomy don’t fit neatly into typical male or female categories.
Why Prevalence Estimates Vary So Widely
Two figures dominate this debate. The higher one, 1.7%, comes from biologist Anne Fausto-Sterling and has been widely cited in academic papers and media. It includes a broad range of conditions: chromosomal variations like Klinefelter syndrome (an extra X chromosome in males) and Turner syndrome (a missing X chromosome in females), as well as late-onset forms of adrenal hyperplasia that may cause no visible differences at birth.
The lower figure, 0.018%, comes from a 2002 response by physician Leonard Sax, who argued that most clinicians would not classify many of those conditions as intersex. His narrower definition focuses on cases where the body’s physical sex characteristics are visibly ambiguous or clearly at odds with the person’s chromosomes. Under that stricter lens, intersex conditions affect roughly 1 in 5,500 births.
Neither number is “wrong” exactly. They answer different questions. If you’re asking how many people have any variation in sex chromosomes, hormones, or reproductive anatomy, the broader figure is more relevant. If you’re asking how many newborns have visibly ambiguous genitalia or a clear mismatch between their chromosomes and their body, the narrower figure applies.
The Rarest Form: Ovotesticular DSD
What was historically called “true hermaphroditism,” now known as ovotesticular DSD, is the condition most people picture when they hear the word. A person with ovotesticular DSD has both ovarian and testicular tissue, sometimes in the same organ. This is genuinely rare, occurring in an estimated 1 in 100,000 births. It accounts for only a small fraction of all intersex conditions.
More Common Intersex Variations
Most intersex traits fall into categories that are individually uncommon but collectively add up. Here are some of the better-studied ones:
- Klinefelter syndrome (47,XXY): Affects about 1 in 650 male newborns. Boys and men with this chromosomal pattern often have lower testosterone, may develop some breast tissue during puberty, and frequently discover the condition only when tested for infertility. Many go through life without knowing they have it.
- Congenital adrenal hyperplasia (CAH): The classic form occurs in roughly 1 in 9,500 births worldwide, though rates vary by region. Countries in the Eastern Mediterranean and South-East Asia have the highest incidence. CAH causes the adrenal glands to produce excess androgens, which can result in ambiguous genitalia in newborn girls. Milder, late-onset forms are more common and may not cause visible differences at birth.
- Androgen insensitivity syndrome (AIS): Classified as a rare disease by the National Institutes of Health. Complete AIS affects roughly 1 in 20,000 to 1 in 99,000 people with XY chromosomes. In this condition, the body’s cells don’t respond to testosterone, so a person with male chromosomes develops female external anatomy. Many people with complete AIS are raised as girls and don’t learn about the condition until puberty, when menstruation doesn’t start.
When Intersex Traits Are Discovered
Some intersex conditions are obvious at birth because a baby’s genitalia don’t look typically male or female. These are the cases that get immediate medical attention. But a significant number of intersex variations aren’t detected until much later. Klinefelter syndrome, for instance, often goes undiagnosed until a man in his 30s or 40s seeks help for infertility. Complete androgen insensitivity syndrome commonly surfaces during adolescence when a teenager with a typically female appearance doesn’t get a period. Late-onset adrenal hyperplasia may show up as unusual hair growth or irregular cycles in young women.
This delayed discovery is one reason prevalence is hard to pin down. Many people with milder intersex traits never receive a formal diagnosis at all.
Why the Terminology Changed
“Hermaphrodite” in biology refers to organisms that have fully functional male and female reproductive systems at the same time, like certain snails, earthworms, and fish. Humans don’t work this way. Even in ovotesticular DSD, the most analogous condition, both types of tissue are rarely fully functional. The term was formally replaced in clinical medicine after a 2006 consensus statement defined these conditions as “disorders of sex development,” later softened by many advocacy groups to “differences of sex development.”
The shift wasn’t just about precision. Many people with intersex traits found the old term dehumanizing, and the medical community acknowledged that it carried stigma that could harm patients. You’ll still see “hermaphrodite” in older medical literature, but current practice avoids it.
Putting the Numbers in Perspective
If you use the broadest definition, intersex traits are roughly as common as red hair. If you use the narrowest clinical definition, they’re closer in frequency to cystic fibrosis. The condition most people imagine when they search this question, a person born with both ovarian and testicular tissue, is among the rarest variations at 1 in 100,000. But the full spectrum of ways human sex development can vary is much wider than most people realize, and far more common than that single rare condition suggests.