Endometriosis is a common cause of pelvic pain. Normally, during the menstrual cycle tissue builds up and breaks down within the uterus. In endometriosis, endometrial tissue (tissue from the lining of the uterus) is found outside the uterus. During the menstrual cycle this tissue builds up and breaks down in the same way but there is no way for it to leave the body. These areas bleed internally, causing irritation, inflammation, and scarring.
Women with endometriosis have symptoms ranging from mild to severe, although some women have no symptoms at all.

Symptoms can include menstrual cramps, pain during intercourse, low back pain, constipation, pain with bowel movements, and infertility.