A condition in which endometrium (the cells lining the interior of the UTERUS) is found in other parts of the body. The most common site of such misplaced endometrium is the muscle of the uterus. The next most common site is the ovary (see OVARIES), followed by the PERITONEUM lining the PELVIS, but it can occur anywhere in the bowel. The main symptoms are MENORRHAGIA, DYSPAREUNIA, painful MENSTRUATION and pelvic pain. Treatment is usually by removal of the affected area using a laparoscope, but in some cases satisfactory results are obtained from the administration of PROGESTOGENS such as NORETHISTERONE, norethynodrel and DANAZOL. Recurrence may occur, even after apparently successful surgery.