Endometriosis. Light micrograph of a section through an ovary showing endometriosis. Endometriosis is a condition where detached parts of the uterus lining (endometrium) move to other sites in the body. The cysts that result (centre) bleed during menstruation, causing pain, inflammation and scarring. Endometriosis is fairly common, affecting perhaps 10% of women. It is hard to diagnose, requiring surgical insertion of a laparoscope into the abdomen. It can be treated with various drugs or with surgical removal of the cysts.