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Abstract In shear wave elastography (SWE) studies, the optimal cutoff value of Young’s modulus for the diagnosis of benign and malignant thyroid nodules varies greatly, which affects the clinical application of the method. The objective of this study was to evaluate the influence of thyroid nodule size on the clinical diagnostic efficacy of SWE. A total of 356 thyroid nodules of 280 patients were divided into three groups according to size (Group A: ≤ 1 cm; Group B: 1–2 cm; Group C: ≥ 2 cm). SWE was used to measure the maximum Young's modulus (Emax) values of all thyroid nodules. Receiver operating characteristic (ROC) curves were drawn with pathological results as the gold standard. For all nodules, the optimal cutoff value of Emax in SWE for diagnosing malignant thyroid nodules was 36.2 kPa. The sensitivity and specificity were 76.5% and 78.4%, respectively. Groups A, B, and C had different optimal Emax cutoff values of 33.7 kPa, 37.7 kPa, and 55.1 kPa, respectively. The area under the ROC curve (AUC) values of Groups A, B, and C (0.844, 0.886, and 0.935, respectively) were all greater than the values for all lesions (0.830). The specificity values of Groups A, B, and C (86.4%, 82.6%, and 88.2%, respectively) were all increased, and the sensitivity values of Groups B and C (89.7% and 96.4%, respectively) were also increased compared with the values for all lesions. Thyroid nodule size affects the optimal Emax cutoff value of SWE. We suggest that different cutoff values be used to diagnose benign and malignant thyroid nodules according to lesion size.