Background/Aim. Ovarian cancer is the leading cause of death from gynecologic malignancies. Risk of malignancy index (RMI) is recommended in assessment of patients with adnexal masses. The aim of this study was to verify the effectiveness of the RMI in the discrimination between benign lesions and malignant adnexal masses in clinical practice. Methods. Ultrasounds were performed for all the patients and menopausal status, CA125 level and calculated RMI were defined. All the patients were divided into 3 groups depending on RMI (< 25, 25-200, > 200). After operations all adnexal masses were analyzed histopathologically (HP) and then sensitivity, specificity and predictive value of RMI were calculated. Results. Out of a total of 81 patients involved benign tumor had 51 (62.96%) and malignant 30 (37.04%) of the patients. The average value of CA125 in the group of patients with benign adnexal masses was 68.3 U/mL and in the group of patients with malignant adnexal masses it was 581.95 U/mL. In the group of patients with benign adnexal masses the average RMI was 284.9 and in the group of patients with malignant adnexal masses RMI was 469.2. All the results showed a positive correlation between both HP categories and RMI categories. The more malignant HP result produced higher RMI and the cut off value was RMI = 200. Sensitivity of RMI was 83.33%, specificity was 94.12%, positive predictive value was 89.29% and negative predictive value was 90.57%. Conclusion. Our study showed that RMI is very reliable in differentiation benign from malignant adnexal masses.