Objective. The purpose of this study was to describe a new reporting system called the Gynecologic Imaging Reporting and Data System (GI-RADS) for reporting findings in adnexal masses based on transvaginal sonography. Methods. A total of 171 women (mean age, 39 years; range, 16-77 years) suspected of having an adnexal mass were evaluated by transvaginal sonography before treatment. Pattern recognition analysis and color Doppler blood flow location were used for determining the presumptive diagnosis. Then the GI-RADS was used, with the following classifications: GI-RADS 1, definitively benign; GI-RADS 2, very probably benign; GI-RADS 3, probably benign; GI-RADS 4, probably malignant; and GI-RADS 5, very probably malignant. Patients with GI-RADS 1 and 2 tumors were treated expectantly. All GI-RADS 3, 4, and 5 tumors were removed surgically, and a definitive histologic diagnosis was obtained. The GI-RADS classification was compared with final histologic diagnosis. Results. A total of 187 masses were evaluated. The prevalence rate for malignant tumors was 13.4%. Overall GI-RADS classification rates were as follows: GI-RADS 1, 4 cases (2.1%); GI-RADS 2, 52 cases (27.8%); GI-RADS 3, 90 cases (48.1%); GI-RADS 4, 13 cases (7%); and GI-RADS 5, 28 cases (15%). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 92%, 97%, 85%, 99%, and 96%, respectively. Conclusions. Our proposed reporting system showed good diagnostic performance. It is simple and could facilitate communication between sonographers/ sonologists and clinicians. Key words: adnexal mass; reporting system; sonography. ransvaginal sonography (TVS) has become the first-step imaging technique for characterizing adnexal masses. When used by experienced examiners, this technique achieves high sensitivity for identifying ovarian cancer, and it has been shown to be useful for selecting the best surgical approach. [1][2][3] However, despite the tremendous progress in the diagnostic capability of TVS, a large multicenter study reported that the false-positive rate could be as high as 24%. 4 One explanation for this high false-positive rate may be operator experience, as has been shown in a recent randomized trial.5 Another reason could be a problem in the transmission of information about findings from the sonologist or sonographer to the clinician who makes final decision. As a matter of fact, reports describing sonographic findings are sometimes confusing.