Why endometrial tissue appears outside the uterus is unknown.
Endometriosis can impair fertility and cause pain (particularly before and during menstrual periods and during sexual intercourse), but it may cause no symptoms.
Doctors check for endometrial tissue by inserting a thin viewing tube through a small incision near the navel (laparoscopy).
Drugs are used to relieve pain and to slow the growth of the misplaced tissue.
Surgery may be done to remove the endometrial tissue outside the uterus and sometimes to remove the uterus and the ovaries.

Endometriosis is a chronic disorder that may be painful. Exactly how many women have endometriosis is unknown because it can usually be diagnosed only by directly viewing the endometrial tissue (which requires a surgical procedure, typically laparoscopy). About 6 to 10% of all women have endometriosis. The percentage of women who have endometriosis is higher among women who are infertile (25 to 50%) and women who have chronic pelvic pain (75 to 80%). The average age at diagnosis is 27, but endometriosis can develop in adolescents.
Common locations of misplaced endometrial tissue (called implants) include the following:

Ovaries
Ligaments that support the uterus
The space between the rectum and vagina or cervix and the space between bladder and uterus

Less common locations include the fallopian tubes, the outer surface of the small and large intestines, the ureters (tubes leading from the kidneys to the bladder), the bladder, and the vagina. Rarely, endometrial tissue grows on the membranes covering the lungs (pleura), the sac that envelops the heart (pericardium), the vulva, the cervix, or surgical scars in the abdomen.
The misplaced endometrial tissue responds to hormones as normal endometrial tissue does. Thus, it can bleed and cause pain, particularly before and during menstrual periods. The severity of symptoms and the disorder