Premature ovarian insufficiency (POI) is the loss of function of the ovaries before age 40, characterized by amenorrhea, hypoestrogenism, and elevated serum gonadotropin levels. Endometriosis is defined as the presence of endometrial tissue outside the uterus. Although the etiology of endometriosis remains elusive, retrograde menstruation into the peritoneal cavity during menstruation is widely accepted as a major contributing factor in the pathogenesis of this disease. It is well- known that surgery for ovarian endometriosis can lead to. As far as we know, there is no report of the occurrence of endometriosis in patients with POI. We would like to describe a rare case of a 33 year-old woman, gravida 0, para 0 patient who was admitted to the Department of Obstetrics and Gynecology, Boramae Medical Center for the treatment of endometrioma with POI. She visited the hospital for the first time at the age of 18 in April 2005 with amenorrhea. She was diagnosed for POI through work-up of amenorrhea and hormone treatment was started. She was treated with sequential EP therapy. She and her husband came together to outpatient clinic after marriage on February 2017. The results of repeated hormone test were FSH 70.1, E2 9 and AMH < 0.01. She made an attempt to get pregnant through ovum donation and IVF-ET procedure for 2 times on Second half of 2017, but failed. She came back to our hospital, notified to have left ovarian mass from local clinic. On the pelvis MRI scam, about 2.3 cm sized endometrioma in the left ovary was noted. The patient was admitted and conducted pelviscopic left salpingo-oophorectomy. Entering the peritoneal cavity, left ovarian cyst about 3cm noted, and chocolate like fluid inside was identified. Right ovary was grossly atrophic. There were endometriotic spot on uterine posterior wall, and fulguration was done. She discharged without post-op complication. Pathological reports revealed to endometriotic cyst, left ovary.