Endometriosis is a condition in which the tissue that normally lines the uterus grows outside the uterus.
The word endometriosis comes from the word "endometrium" (pronounced en-doh-MEE-tree-uhm)—endo means "inside" and metrium (pronounced MEE-tree-uhm) means "uterus, where a mother carries her baby.” Health care providers call the tissue that lines the inside of the uterus the endometrium.
For a brief explanation of endometriosis, watch this video interview with NICHD expert Dr. Esther Eisenberg, "Taking Aim at Endometriosis."
Endometriosis Symptoms and Causes: A Meet Our Researchers Video Text Alternative.
Health care providers may use the terms "implants," "nodules," or "lesions" to describe areas or patches of endometriosis. Most endometriosis patches are found in the pelvic cavity:
- On or under the ovaries
- On the fallopian tubes, which carry egg cells from the ovaries to the uterus
- Behind the uterus
- On the tissues that hold the uterus in place
- On the bowels or bladder
In rare cases, endometriosis may grow outside the pelvic cavity, such as on the lungs or in other parts of the body.1
Researchers' understanding of endometriosis is changing as scientific evidence proves and disproves long-held assumptions. For example, researchers used to think that pain from endometriosis was related to the size of the patches growing outside the uterus. But evidence shows that this is not the case. In fact, the size and location of the lesions are not related to the severity of pain or to the location of the pain.2,3 Assessment of quality of life indicates that pain is also not associated with a woman’s ability to get pregnant.4,5
Office on Women's Health, U.S. Department of Health and Human Services. (2009).
Endometriosis fact sheet. Retrieved December 26, 2011, from
Stratton, P., & Berkley, K. J. (2011). Chronic pelvic pain and endometriosis: Translational evidence of the relationship and implications. Human Reproduction Update, 17(3), 327–346.
American College of Obstetricians and Gynecologists. (2010, Reaffirmed 2016). Management of endometriosis (Practice Bulletin No. 114). Obstetrics & Gynecology, 116(1), 223–236. [top]
Santulli, P., Bourdon, M., Presse, M., Gayet, V., Marcellin, L., Prunet, C., et al. (2016). Endometriosis-related infertility: Assisted reproductive technology has no adverse impact on pain or quality-of-life scores.
Fertility and Sterility,105(4), 978–987.
Wilson-Harris, B. M., Nutter, B., & Falcone, T. (2014). Long-term fertility after laparoscopy for endometriosis-associated pelvic pain in young adult women.
Journal of Minimally Invasive Gynecology, 21(6), 1061–1066.
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?