A medical condition in which the tissue that normally lines the uterus, called endometrium, grows in other areas of the body. This can cause irregular bleeding, pain, and sometimes infertility. The tissue can grow on the outside of the uterus, ovaries, and many other areas of the body. Usually the pain is most severe during the days of the month when the endometrium is sloughed off in the woman's cycle, as the tissue which has grown in incorrect areas attempts to do the same thing.

There is some evidence indicating that endometriosis is carried genetically, but it is occuring much more commonly with each generation. Endometriosis is estimated to occur in 10 to 20% of women in their reproductive years, and may be as high as 15 to 40% of infertile women. Adolescents with endometriosis often experience pain, sometimes extreme cramping, but it is usually written off as normal and ignored.

The condition is often treated with drugs that initiate a state of "pseudopregnancy", where the body enters a state resembling pregnancy through hormone treatments, or "pseudo menopausal", where the body enters a state resembling menopause. However, several of the drugs used for this in the past have been found to have side effects making them unusable today. Sometimes, laser burning of the endometrial tissue is done for severe cases. This often solves the problem, but because endometrium can grow in locations outside of the usual scope of laparoscopy, it sometimes isn't enough. Hysterectomy is a final solution.