Endometriosis is described as a chronic inflammatory disease, characterized by endometrial-like tissue, found outside the uterine cavity which cause chronic pelvic pain, infertility,dysmenorrhea. The prevalence of endometriosis is difficult to determine accurately but in asymptomatic women, the prevalence of endometriosis ranges from 2- 22 %, depending on the population studied , in infertile women 20-50 % and in those with pelvic pain, between 40-50% (Balasch, 1996; Eskenazi, 2001; Meuleman, 2009).Endometriosis is found 7-10% of reproductive agewomen and 20-90% in with chronic pelvic pain, infertility cases. Pathogenesis of endometriosis is not yet fully understood but one potential cause of the disease is retrograde menstruation which results in the deposition of endometrial tissue into the peritoneal cavity. Today a composite theory of retrograde menstruation with implantation of endometrial fragments in conjunction with peritoneal factors to stimulate cell growth is the most widely accepted explanation for peritoneal endometriosis. Susceptibility to endometriosis is thought to depend on the complex interaction of genetic, immunologic, hormonal and environmental factors. To determine prevalence and severity of clinical symptoms, compare meta-analysis to changes the clinical value of serum CA-125 and peritoneal fluid cytology in women with endometriosis of Ulaanbaatar city. We had selected total of 60 woman with endometriosis which were registered from January to December 2014 in gynecologic clinic of First Maternity Hospital. The research group registered in questionnaire with 28 questions. During the inspection laboratory analysis of serum CA-125, ultrasound analysis and peritoneal fluid cytology were done. Assessment of pelvic pain by means of a 10-point linear analog scale / pain score/ which provided by International Pain Association. The research result was worked out by prospective method. Average age of patients 33.4±8.9. Pain location: Chronic pelvic pain 30%; Dysmenorrhea 28.3%; Dysparunea 10%; Pain during defecation 6,7%; Without pain -25%. Average level of Serum СА125 was 38.13±20.6. Location of endometriosis: adenomyosis - 8.4%, endometrioma-15% endometriotic lesion at cul de suc 68.3%, rectal involment 1.7%, tubal lesion-3.3%, combined 3,3%. 76.7% of surgery for endometriosis have done by laparoscopy and 23.3% by laparotomy. Ultrasound examination result: endometrioma d=0-2cm-1.7%, d= 3-5cm-36.2%, d=6-8cm-10.3%, d=9cm<-12.1%. Cytology result: Peritoneal fluid contains 75% of erythrocytes, mesothelial cells and it needs to further study.CONCLUSION:Most of patient /58.3%/ had chronic pelvic pain and dysmenorrhea. The severity of pain was significantly improved after operative laparoscopy. /p<0.05%/51,7% of patient had infertility problem.Value of serum CA-125 was higher in study group with large sized and not clear content ovarian endometrioma by ultrasound examination. /p<0.05%/The local environment of peritoneal fluid surrounding the endometriotic implant is immunologically dynamic and links the reproductive and immune systems. Peritoneal factors to stimulate cell growth is the most widely accepted explanation for peritoneal endometriosis. Peritoneal fluid contains a variety of free floating cells, including macrophages, mesothelial cells, lymphocytes, erythrocytes, eosinophils and mast cells. In our cytology results: peritoneal fluid contains 75% of erythrocytes, mesothelial cells.