Introduction: Ovarian cancer is a big health concern, which continually attracts clinical debate in regard to validation and improvement of methods for malignancy prediction in women with adnexal masses. Purpose of investigation: The aim of this study was to evaluate the validity of the risk of malignancy index (RMI) as a diagnostic tool for discrimination between benign and malignant adnexal masses. Materials and Methods: The study group of 153 women with adnexal tumours were investigated and the RMI was calculated for each patient. Results: According to the histological examination of the specimens, 116 (75.8%) women had benign conditions, while 37 (24.2%) women had malignant masses. The RMI was reliable in 85% of all women with adnexal masses, and optimal cut-off value of 200 provides the highest performance for preoperative triage of adnexal masses. Conclusions: Although this study confirmed that the RMI is useful method for preoperative identification of benign and malignant adnexal masses, it is only a diagnostic tool and cannot predict malignancy in all cases.