Background: Adnexal masses are common presentation among gynecological practice. Differentiation of benign than malignant lesions is of utmost importance for treatment plan. The gold standard other than histopathology did not determined yet.  
The aim of the work: The current work aimed to measure the accuracy of the preoperative risk of malignancy index [RMI] in differentiation between benign and malignant adnexal masses.
Patients and Methods: This study included 80 patients, presented with adnexal masses/ovarian cysts. They were managed by surgery, during the period from May 2015 to November 2017. We collected the following data: age, gravidity, menopause status, parity, cancer antigen 125 [CA125] levels and ultrasound results. RMI was calculated according to Tingulstad' model. Postoperatively, histopathology results were documented for every patient and used as the gold standard diagnostic modality to measure predictive power of RMI and CA125.
Results: Malignant lesions were documented in 27.5%, while 72.5% were benign. The benign tumors were significantly associated with younger age than malignant lesions [27.88±7.68 versus 41.05±11.81]. The proportion of postmenopausal women was significantly higher among malignant than benign ovarian lesions [45.5% vs. 1.7%, respectively, p < 0.001]. All ultrasound parameters of RMI were significantly different in malignant than benign masses. The best cutoff points of RMI and CA125 were 90.6 and 20.0 respectively. At such points, RMI had 90.6 sensitivity. However, specificity, positive predictive value, negative predictive values were 68.2%, 75.9%, 51.7% and 86.3%, respectively.
Conclusion: RMI was found to be a significant marker in preoperative evaluation and management of adnexal mass, and was useful for referring patients to tertiary care centers, and advocated for screening purposes.