OBJECTIVES: The aim of this study is to confirm the clinical and histopathologic findings of ovarian tumors and determine the malignancy before operation. It will attribute to early diagnosis, determining direction of treatment and improving prognosis of malignant ovarian tumor. METHODS: Seven hundred sixty-five patients who had an operation for ovarian tumors in the department of Obstetrics and Gynecology of Gachon University Gil Medical Center from April 2007 to December 2009 were enrolled as subjects. A retrospective analysis of age, parity, menopausal status, preoperative CA 125, histology, ultrasound, and treatment method was done. RESULTS: 1. Among benign ovarian tumors, endometrial cyst (211 cases, 30.1%) was most common and had the highest preoperative CA 125 (76.07 U/mL). 2. Among borderline ovarian tumors, mucinous type (16 cases, 62.5%) was most common, but preoperative CA 125 was higher in serous type (144.38 U/mL) than mucinous type (82.59 U/mL). 3. Among malignant ovarian tumors, serous adenocarcinoma (14 cases, 29.8%) was most common, and undifferentiated carcinoma had the highest preoperative CA 125 (500.0 U/mL). 4. The preoperative CA 125 showed a tendency to increase in relation to stage in malignant ovarian tumors. 5. Age, preoperative CA 125, menopausal status and ultrasound finding were identified as discriminating factors for malignancy and relative risk of them were 7.19, 7.90, 5.56 and 61.43, respectively. CONCLUSION: Using the combination of age, menopausal status, preoperative CA 125 and ultrasound to diagnose ovarian tumors before the operation will be a help to early diagnosis and determining the treatment and improve prognosis.