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Background: Thyroid cancer is one of the most common cancers and is especially common in young patients. Therefore, effective recognition and treatment of thyroid cancer are essential for patient survival., Objectives: To compare the effectiveness of standard guidelines for predicting thyroid malignancy. To do so, thyroid nodules were classified according to the categories of the American Thyroid Association (ATA) and Thyroid Imaging Reporting and Data System (TI-RADS) guidelines, and compared with fine-needle aspiration biopsy (FNAB) results., Material and Methods: The study included 1741 thyroid nodules with a final diagnosis in 1121 consecutive patients. The FNAB was recommended for all patients according to ATA guidelines and subsequently performed. The nodules were reclassified according to TI-RADS guidelines., Results: Comparing nodules classified according to ATA and TI-RADS in terms of ultrasonography (US) features with the Bethesda cytological diagnosis classification System for Reporting Thyroid Cytopathology, 37.6% of the nodules classified in the high-risk category according to the ATA classification were found to be malignant cytology, 10.4% suspicious for malignancy, 4% non-diagnostic, 9.6% indeterminant cytology, and 38.4% benign. According to the TI-RADS risk category, 50% of those with high suspicion were malignant, 13.3% suspicious for malignancy cytology and 36.7% were benign. For the TI-RADS guidelines, the best cutoff value for differentiating benign and malignant nodules was found to be 4.5 (area under the curve (AUC) = 0.962, 95% CI = 0.943-0.981, p < 0.001). For the ATA guidelines, the best cutoff value for separating benign and malignant nodules was 4.5 (AUC = 0.917, 95% CI = 0.875-0.959, p < 0.001). The diagnostic performances of the TI-RADS and ATA score systems were evaluated using highly suspicious nodules. The sensitivity and specificity of highly suspicious nodules, according to both TI-RADS and ATA guidelines, were both high. Sensitivity and specificity of ATA classification were 80% and 96.3%, respectively. Sensitivity and specificity of TI-RADS classification were 76% and 97.5%, respectively, but positive predictive value was low (63.3% compared to 55.5%)., Conclusions: Both, the ATA and TI-RADS classifications can effectively predict malignancy risk of thyroid nodules and may thus decrease unnecessary FNAB.