Endometriosis is a gynecological medical condition in women in which endometrial-like cells appear and flourish in areas outside the uterine cavity. Endometriosis occurred within the ovary is also known as chocolate cyst. Adenomyosis, another kind of endometriosis, usually refers to ectopic endometrial tissue (the inner lining of the uterus) within the myometrium (the thick, muscular layer of the uterus). The uterine cavity is lined by endometrial cells, which are under the influence of female hormones. These endometrial-like cells in areas outside the uterus (endometriosis) are influenced by hormonal changes and respond in a way that is similar to the cells found inside the uterus. Endometriosis is a condition where tissue similar to the lining of the uterus is found elsewhere in the body. In general, it can be found anywhere in the pelvic cavity: on the ovaries, the fallopian tubes, and on the pelvic sidewall. Endometriosis is a kind of benign disease.