Objective:To explore the added value of the Copenhagen index(CPH-I) in the diagnosis of adnexal masses with ovarian-adnexal reports and data systems (O-RADS) and the International Ovarian Tumor Analysis (IOTA) simple rules. Methods:The ultrasound images of 179 adnexal masses confirmed by pathological results were analyzed retrospectively in the First People's Hospital of Chuzhou,Anhui from October 2023 to October 2025. The O-RADS classification and IOTA simple rule were used for classification evaluation respectively,and CPH-I of each patient was calculated. Using pathological results as the gold standard,the optimal cutoff value for each diagnostic method was obtained by Youden index. The diagnostic efficacy of the two ultrasound models alone and in combination with CPH-I was compared. The diagnostic efficacy of O-RADS 4 masses and IOTA uncertain masses combined with CPH-I was calculated,too. Delong test was used to compare the area under the curve(AUC) of receiver operating characteristic curve for each model.Results:The optimal cutoff value for O-RADS diagnosis was O-RADS 4 tumors,the optimal cutoff value for IOTA simple rule diagnosis was uncertain masses,and the optimal cutoff value for CPH-I diagnosis was −2.165. The AUC values of O-RADS,IOTA simple rules,and CPH-I for the diagnosis of adnexal masses were 0.866,0.926 and 0.886,respectively. The AUC values of the two ultrasound models combined with CPH-I were 0.861 and 0.902,respectively. When CPH-I was applied separately to O-RADS 4 masses and IOTA uncertain masses,the AUC were 0.933 and 0.941,respectively,which were higher than those of O-RADS and IOTA simple rules alone(P=0.022,P=0.562). Conclusion:CPH-I has good added value to O-RADS and IOTA simple rules in diagnosing adnexal masses,especially when applied to O-RADS 4 masses and IOTA uncertain masses,which were with the best diagnostic performance.