One very important cause of infertility is endometriosis. This is a condition where the endometrium or lining of the uterus is formed at sites outside the uterus. This commonly involves the ovaries, pelvis , uterosacral ligaments, peritoneum. It causes severe pain during menses, pain during intercourse and infertility. Long standing endometriosis causes endometriotic cysts in case of ovarian involvement. Endometriosis seen in the wall of the uterus is called adenomyosis. Treatment involves both surgical and medical therapies.