Endometriosis is defined as the presence of endometrial tissue outside the uterine cavity. Common sites include; - Ovaries (most common site. Ovarian endometriosis is also known as endometriomas or chocolate cysts) - Pouch of Douglas - Posterior broad ligaments - Uterosacral ligaments - Fallopian tubes - Sigmoid colon - Appendix - Bladder - Vagina