Endometriosis is a medical condition in which the tissue that normally lines the inside of woman's uterus abnormally grows outside of this reproductive organ. Certain women with this condition can develop endometriosis cysts within the ovaries, which are referred to as endometriomas.

Endometriosis is the presence of endometrial tissue, the tissue that lines the uterus, in places outside the uterus. Endometrial tissue can spread as far as the brain, but one of the most common sites for endometrial implants is the uterosacral ligament, located behind the cervix.

Endometriosis is the migration of endometrial tissue, the tissue that lines the inside of the uterus, to areas outside the uterus.

Most cases of endometriosis involve the pelvic area, according to A. M. Wolthuis, C. Aelvoet, J. Bosteels and J. P. Vanrijkel in a 2003 article in the journal "Acta chir belg." However, the condition can occur in other parts of the body as well, with symptoms that intensify with the menstrual cycle.