Endometriosis is characterized by development of the endometrial tissue outside the uterus like ovary, pelvic peritoneum, pelvic organs, and affects 6-10% of reproductive-aged women. The prevalence of endometrioma is 17-44% of women with endometriosis. Since endometriosis is mainly a disease for the women at their reproductive ages, it is important to consider ovarian reserve when managing the cases with ovarian endometriosis. There has been a long debate whether the endometrioma per se decreases the ovarian reserve and/or surgery for endometrioma - either by laparoscopy or by laparotomy - decreases it. Although the dispute for these questions is not totally settled down, in this article, we would like to give some clues for the answers in view of the literature.