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OBJECTIVE. The purposes of this study were to identify the similarities and differences among the Korean Thyroid Imaging Reporting and Data System (TIRADS), American College of Radiology (ACR) TI-RADS, and European TIRADS and to compare the diagnostic performance of sonographic fine-needle aspiration (FNA) criteria for detecting malignant thyroid nodules. MATERIALS AND METHODS. This study included 2274 consecutively evaluated thyroid nodules 1 cm or larger in 1836 patients with final diagnoses from January 2011 to December 2016. US features of the nodules were retrospectively reviewed and classified according to three published guidelines from international societies. We compared the US lexicons, categories, and diagnostic performance of the FNA criteria for malignant nodules among the three reporting systems. RESULTS. Of the 2274 thyroid nodules, 1974 (86.8%) were benign and 300 (13.2%) were malignant; 93.7% of all malignancies were papillary carcinoma. Most of the US lexicons were similar among the three systems except for the definition of echogenicity of a nodule of mixed echogenicity in European TIRADS. Although the categories had strong correlations ( r = 0.777-0.877, all p < 0.001) among the three systems, significant differences were observed in categories 5, 4, and 3 of nodules (all p < 0.001) and in the sensitivity, specificity, and rate of unnecessary FNA of the FNA criteria for malignancy (all p < 0.001). CONCLUSION. Although the three systems had similarities in most US lexicons, significant differences were observed in the classified categories and diagnostic performance of the FNA criteria for malignancy.