Endometriosis is a gynecological condition in which the tissue that normally lines the woman’s uterus grows outside of the uterus, often causing pain. Endometriosis is a common condition, particularly among women of childbearing age. It affects an estimated 2 to 10% of American women in that age group. Endometriosis can be a debilitating disease for some women who feel ongoing pain, while others may not have any symptoms. It is also a factor in infertility. The condition name comes from the word "endometrium," which is the tissue that lines the uterus. During a woman's regular menstrual cycle, this tissue builds up and is shed if she does not become pregnant. Women with endometriosis develop tissue that looks and acts like endometrial tissue outside the uterus, usually on other reproductive organs inside the pelvis or in the abdominal cavity. Each month, this misplaced tissue responds to the hormonal changes of the menstrual cycle by building up and breaking down just as the endometrium does, resulting in internal bleeding. Unlike menstrual fluid from the uterus that is shed by the body, blood from the misplaced tissue has nowhere to go. This causes the tissues surrounding the endometriosis to become inflamed or swollen. This process can produce scar tissue around the area, which may develop into lesions or growths. In some cases, particularly when an ovary is involved, the blood can become embedded in the tissue where it is located. It may then form blood blisters that become surrounded by a fibrous cyst. Endometriosis is most often found in the ovaries. But it can also be found in other places including the fallopian tubes, ligaments that support the uterus, the internal area between the vagina and rectum, the outer surface of the uterus, and in the lining of the pelvic cavity. It can also spread to the intestines and other areas of the abdominal cavity. Endometriosis is considered a major cause of female infertility. In mild to moderate cases, the infertility may be just temporary. In these cases, surgery to remove adhesions, cysts, and scar tissue can restore fertility. In a very small percentage, women may remain infertile. The cause of endometriosis is still unknown. One theory suggests that during menstruation some of the tissue backs up through the fallopian tubes into the abdomen, a sort of “reverse menstruation,” where it attaches and grows. Another theory states that certain families may have predisposing genetic factors to the disease. Current research is also looking at the role of the immune system in activating cells that may secrete factors that stimulate endometriosis. While any woman may develop endometriosis, the following women seem to be at an increased risk for the disease: women who have a first-degree relative (mother, sister, or daughter) with the disease, women who have never given birth, and women with an abnormal uterus. For many women, simply having a diagnosis of endometriosis brings relief. Diagnosis begins with a gynecologist evaluating a patient's medical history and a complete physical examination including a pelvic exam. A diagnosis of endometriosis can only be certain when the physician performs a laparoscopy. A laparoscopy is a minor surgical procedure in which a laparoscope (a thin tube with a lens and a light) is inserted into an incision in the abdominal wall. Using the laparoscope to see into the pelvic area, the physician can often determine the locations, extent, and size of the endometrial growths. Other tests that may help in diagnosing endometriosis include biopsy, ultrasound, computed tomography (CT or CAT scan), and magnetic resonance imaging (MRI). In general, treatment for endometriosis may include “watchful waiting” to observe the course of the disease, pain medication, and hormone therapy. Sometimes a combination of therapies is used, such as conservative surgery (laparoscopy) with hormone therapy.