Illustration of an ovarian cyst (endometrioma, upper right) and endometrial-like tissue in the pelvic cavity. Endometriosis is a medical condition where cells similar to those of the uterus lining (darker pink, purple) start to grow outside the uterus. It usually occurs in the reproductive organs in the pelvis or abdomen, such as the ovaries, fallopian tubes, pelvic lining, or the surface of the uterus. The tissue growing in these areas does not shed during menstruation like healthy tissue within the uterus, leading to the build-up of abnormal tissue that can cause inflammation, scarring and painful cysts. Common symptoms of endometriosis are painful menstrual cramps and pain during intercourse. Although there is no cure for endometriosis, hormone therapy and pain management can be used to control symptoms. In some cases, laparoscopy (keyhole surgery) may be necessary for those with advanced endometriosis.