A woman holding her abdomen in pain.

How many people are affected by or at risk for endometriosis?

It is difficult to know exactly how many women have endometriosis because some women might have the condition but not the symptoms. In 2011, the NICHD-led Endometriosis: Natural History, Diagnosis, and Outcomes Study found that the number of women with endometriosis varied depending on the population of women being studied and the diagnostic measures that are used.1

The study found that 11% of a group of women who had not been diagnosed with endometriosis actually had the disorder. If this finding applies to all the women in the United States, the number of American women with endometriosis may well exceed previous estimates of 5 million.

Endometriosis is most common in women in their 30s and 40s,2 but it can affect any female who menstruates.

Studies show that women are at higher risk for endometriosis if their:

  • Mother, sister, or daughter had endometriosis (raises the risk about sixfold)2
  • Periods started at an early age (before age 11)3
  • Monthly cycles are short (less than 27 days)3
  • Menstrual cycles are heavy and last more than 7 days3

Studies also show that some factors may lower the risk for endometriosis, including:

  • Pregnancy
  • Starting menstruation late in adolescence4
  • Regular exercise of more than 4 hours a week3
  • Low amount of body fat


  1. Buck Louis, G. M., Hediger, M. L., Peterson, C. M., Croughan, M., Sundaram, R., Stanford, J., et al. (2011). Estimated incidence of endometriosis by diagnostic method and study population: The ENDO Study. Fertility and Sterility, 96(2), 360–365. Retrieved August 17, 2016, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3143230 [top]
  2. American College of Obstetricians and Gynecologists. (2011). Endometriosis. Retrieved December 10, 2015, from http://www.acog.org/~/media/For%20Patients/faq013.ashx External Web Site Policy [top]
  3. American College of Obstetricians and Gynecologists. (2010). Management of endometriosis (Practice Bulletin No. 114). Obstetrics & Gynecology, 116(1), 223–236. [top]
  4. Treloar, S. A., Bell, T. A., Nagle, C. M., Purdie, D. M., & Green, A. C. (2010). Early menstrual characteristics associated with subsequent diagnosis of endometriosis. American Journal of Obstetrics & Gynecology, 202, 534.e1–534.e6. [top]

What causes endometriosis?

How many people are affected by or at risk for endometriosis?

What are the symptoms of endometriosis?

How do health care providers diagnose endometriosis?

What are the treatments for endometriosis?

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