Objective: The aim of this study was to assess the prognostic values of risk of malignancy index (RMI IV), ultrasound score, menopausal status, and serum CA125 and CA19-9 level in patients with borderline ovarian tumor (BOT). Methods: Fifty women having borderline ovarian tumor (BOT) and 5O individuals with benign adnexal mass were enrolled in this retrospective study. The sensitivity, specificity, positive predictive values, negative predictive values and diagnostic accuracy of preoperative serum levels of the CA125 and CA19-9, ultrasound findings and menopausal status, and RMI IV were calculated for prediction of discrimination between BOTs and benign adnexal masses and the results were compared. Results: The RMI IV was the best method for discrimination between BOTs and benign adnexal masses and was more accurate than the other parameters. When Receiver Operator Characteristic area under the curves for menopausal status was analyzed, serum CA 125 and CA19-9 level, ultrasound score, RMI IV(CA125), and RMI IV(CA19-9) were, 0.580, 0.625, 0.548, 0.694, 0.734 and 0.711, respectively. The best RMI IV cut-off was found to be 200 for discrimination of benign and BOT lesions. In the RMI formulation, replacing CA125 with CA19-9 didn't affect RMI IV sensitivity and specificity for discrimination. Conclusion: Compared to ultrasound, menopausal status, CA-125, CA19-9, the RMI IV was found to be the best predictive method for differentiation of BOTs from benign adnexal masses. RMI IV cut-off value of 200 is suitable for differentiation of benign and BOT's.