Objective:To compare the diagnostic accuracy of International Ovarian Tumor Analysis (IOTA) simple rules and risk of malignancy index (RMI 1/RMI 2) scoring to discriminate between benign and malignant adnexal masses.Methods: Secondary analysis of a cohort of patients scheduled for surgery for adnexal masses in a tertiary center between April 2010 and March 2018. Ultrasound examinations were performed by general gynecologists within 24 hours prior to surgery to evaluate sonographic features. Demographic data and preoperative CA 125 levels were recorded. IOTA rules and RMI scoring were applied to predict malignancy and prospectively recorded. Final diagnosis was based on pathological or intraoperative diagnosis. Results:A total of 479 masses met the inclusion criteria and were retrieved from the database: 334 (69.7%) benign and 145 (30.3%) malignant. IOTA rules could be applied to 392 (81.8%) masses and were inconclusive in 87 (18.2%). Sensitivity and specificity of IOTA rules (83.8% and 92.0%, respectively) were significantly higher than RMI 1 (77.2% and 86.8%, respectively) and RMI 2 (82.1% and 82.6%, respectively).Conclusion: IOTA simple rules had higher diagnostic accuracy compared with RMI to discriminate between benign and malignant adnexal masses; however, nearly 20% of IOTA results were inconclusive and needed expert consultation. K E Y W O R D SBenign adnexal mass; International Ovarian Tumor Analysis (IOTA) simple rules; Malignant adnexal mass; Risk of malignancy index (RMI); Ultrasound