To assess the ability of the risk of malignancy index (RMI) based on a serum CA125 level, ultrasound findings and menopausal status, to discriminate benign from malignant adnexal masses.Between September 2002 and November 2004, 296 women with adnexal masses were enrolled. The sensitivity, specificity, positive (PPV) and negative predictive values (NPV) of the CA125 serum level, ultrasound findings and menopausal status in prediction of ovarian cancer were calculated and compared individually or combined into the RMI.The RMI identified malignant cases more accurately than any individual criterion in diagnosing ovarian cancer. Using a cut-off level of 153 to indicate malignancy, the RMI showed a sensitivity of 76.4%, a specificity of 77.9%, a PPV of 65.9%, a NPV of 85.5% with 79.4% correct diagnosis rate.The RMI is an appropriate method in diagnosing adnexal masses with high risk of malignancy and forwarding to gynecological oncology centers for suitable surgical operations.