Ovarian cancer is a common gynecological malignant tumor. Early diagnosis is important for the prognosis of patients with ovarian cancer. To evaluate the accuracy of the Copenhagen Index (CPH‐I) in detecting malignant adnexal tumors and to compare the diagnostic accuracy of CPH‐I and the Risk of Ovarian Malignancy Algorithm (ROMA). PubMed, Web of Science, and Cochrane Library databases were used to retrieve eligible studies. The overall sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and area under the (summary receiver operating characteristic) curve (AUC) were 0.81, 0.88, 6.61, 0.22, 30.43, and 0.91, respectively, in diagnosing malignant adnexal tumors. In addition, using ROMA, the sensitivity, specificity, and AUC were 0.83, 0.85, and 0.90, respectively. CPH‐I showed high accuracy in diagnosing malignant adnexal tumors, which could be an alternative method with similar efficacy to ROMA. CPH‐I was more advantageous in diagnosing adnexal tumors in postmenopausal women.