Endometriosis is a condition characterised by the presence of endometrial tissue (comprising endometrial stroma and glands) outside the uterus. The endometrial tissue may be deposited in the pouch of Douglas, on the uterosacral ligaments, pelvic peritoneum, the uterine wall, cervix, bladder,or ovaries. There may be some found at distant sites such as abdominal laporotomy scars and very rare, the lungs.