Endometriosis is not rare. It affects roughly 10% of women and girls of reproductive age worldwide, which translates to about 190 million people globally and 6.5 million in the United States alone. That makes it about as common as diabetes. The perception that it’s rare stems largely from how often it goes undiagnosed or misdiagnosed, not from how frequently it actually occurs.
How Common Endometriosis Actually Is
The most widely cited figure, from the World Health Organization, puts endometriosis prevalence at 10% of reproductive-age women. Some researchers place the number slightly higher, at around 11%, noting that 1 in 9 women in the U.S. and Australia will have endometriosis in their lifetime. These are conservative estimates because they rely on confirmed diagnoses, and many people with endometriosis never receive one.
The true number is almost certainly higher. When surgeons perform unrelated procedures on women with no endometriosis symptoms, they still find it at notable rates. In one study of women undergoing tubal ligation with no known history of the condition, about 23% had endometriosis in their fallopian tubes that had never been detected. These “silent” cases never enter the prevalence statistics because no one was looking for them.
Why It Seems Rarer Than It Is
The average time from first symptoms to diagnosis is roughly 7.5 to 10 years, depending on the country. In the UK, recent data shows this delay has actually worsened over time, climbing from about 7.5 years in 2020 to closer to 10 years now. During that entire gap, patients are living with the condition but aren’t counted in any statistics.
Misdiagnosis is a major part of the problem. Endometriosis symptoms overlap with irritable bowel syndrome, urinary tract infections, ovarian cysts, and other pelvic conditions. One study examining suspected endometriosis cases found that nearly 47% were initially misdiagnosed, meaning conditions that mimicked endometriosis were confused for it, and vice versa. The symptoms (painful periods, chronic pelvic pain, pain during sex, digestive issues) are common enough that clinicians often attribute them to something else for years before endometriosis is considered.
There’s also a cultural factor. Painful periods have been normalized for so long that many people delay seeking care, and when they do, their pain is sometimes dismissed. This compounds the diagnostic delay and keeps reported prevalence numbers artificially low.
Prevalence in Specific Groups
Endometriosis is far more common in certain populations than the 10% average suggests. Among adolescents with chronic pelvic pain that doesn’t respond to standard treatments like pain relievers or hormonal birth control, nearly 70% turn out to have endometriosis when evaluated surgically. That finding is important because it shows the condition isn’t limited to adults, and severe period pain in teenagers deserves serious clinical attention.
People struggling with infertility also have significantly higher rates. Estimates vary, but endometriosis is found in 25% to 50% of women being evaluated for fertility problems, making it one of the most common underlying causes of difficulty conceiving.
Where Endometriosis Grows Matters Too
Most endometriosis involves tissue growing on or near pelvic organs like the ovaries, fallopian tubes, and the lining of the pelvic cavity. This is what clinicians typically look for. But endometriosis can also appear in unexpected locations, and these cases are genuinely uncommon.
Diaphragmatic endometriosis, where tissue grows on the muscle separating your chest from your abdomen, occurs in about 4.7% of endometriosis patients. It often causes shoulder or chest pain that worsens around menstruation, a symptom pattern most people wouldn’t connect to a gynecological condition. About 6% of people with diaphragmatic endometriosis have no symptoms at all.
Even rarer forms have been documented in the lungs, kidneys, and skin, though these are uncommon enough to appear mostly in case reports. So while endometriosis itself is common, certain locations where it can grow are genuinely rare.
The Cost of Being “Not Rare” but Underfunded
Despite affecting more than 1 in 10 women, endometriosis receives strikingly little research funding. The National Institutes of Health allocates roughly $2 per patient per year to endometriosis research, which represented just 0.038% of the total 2022 health budget. For context, conditions affecting similar numbers of people receive many times that amount.
The financial burden on patients and the healthcare system is substantial. Endometriosis costs an average of about $10,000 more per patient per year in direct medical expenses compared to people without the condition, plus another $2,100 in lost productivity from missed work and reduced functioning. Across the U.S., the total economic impact has been estimated at $22 billion annually, with the majority going toward direct medical care like surgeries, imaging, and specialist visits.
This disconnect between how common the condition is and how little attention it receives helps explain why so many people with endometriosis feel their experience is dismissed or misunderstood. The condition is common. The recognition, funding, and timely diagnosis of it are what remain rare.