Endometriosis is when cells that normally form tissue to line the uterus become implanted on surfaces beyond the outside of the uterus, such as the abdominal cavity, ovaries, bowel, and nearby organs. This tissue sheds monthly, usually in sync with your menstrual cycle, usually causing pain. If the tissue has formed on organs that were not removed during a partial or total hysterectomy, it is possible to develop endometriosis.