INTRODUCTION: We evaluated ultrasonography (US) features of thyroid nodules ≤ 1 cm and > 1 cm and determined the features that might predict malignancy, also aimed to develop a new scoring system considering US features to avoid unnecessary fine-needle aspiration biopsy (FNAB), particularly for subcentimeter nodules. METHODS: We retrospectively evaluated 2233 nodules of 1118 patients who underwent thyroidectomy. US features predictive for malignant histopathology were evaluated by multivariate logistic regression analysis. A US index score was calculated for each nodule considering these features. Results: 337 (15.11%) nodules were ≤1 cm, and 1896 (84.89%) were > 1 cm. In total, 173 (51.33%) of the ≤1 cm nodules were histopathologically benign, and 164 (48.67%) were malignant. Anteroposterior/transverse diameter (AP/T) ≥1, microcalcifications, macrocalcifications, and hypoechoic patterns were significantly more frequent in ≤1 cm malignant compared with benign nodules. Microcalcification, macrocalcification, hypoechoic and iso-hypoechoic patterns, and solid texture were significantly higher in the malignant than the benign group in > 1 cm nodules. The best cut-off of US index scores for discrimination of benign and malignant nodules were > 2 and > 4 for ≤1 cm and > 1 cm nodules, respectively. DISCUSSION AND CONCLUSION: Our US scoring system may help clinicians and surgeons to select nodules for FNAB more accurately, particularly those sub-centimeter in size.