Endometriosis is a condition where tissues similar to those lining the cavity of the uterus are present outside the actual lining of the uterus. It may be found in the muscles of the uterus (Adenomyosis) around the Fallopian tubes, on the surface of the bowel, bladder, peritoneal surfaces in the abdomen and pelvis and sometimes rarely in the vagina and lungs. These deposits shed under the influence of the hormones produced by the ovaries (oestrogen and progesterone) in a similar fashion to the shedding of the lining of the uterus during the menstrual period. This results in bleeding at the various sites, causing scarring or adhesions to form.