Purpose: Fine needle aspiration is a safe and relatively accurate procedure for distinguishing benign and malignant lesions. We determined the diagnostic value of ultrasoundguided fine needle aspiration using an extension tube and examination by an endocrine surgeon. Methods: We reviewed the medical records of 257 consecutive patients receiving surgery for thyroid nodules in the Department of Surgery, Jesus Hospital, from January, 2006, to August, 2008. All patients received ultrasound-guided fine needle aspiration with an extension tube. Results: The male to female ratio was 1：5.5. Definitive histopathological diagnosis revealed benign lesions in 120 cases (47%) and malignant lesions in 137 cases (53%). Benign lesions were composed of nodular goiter (102 cases), follicular adenoma (13 cases), and Hashimoto thyroiditis (5 cases). Malignant lesions were composed of papillary carcinoma (131 cases) and follicular carcinoma (6 cases). Fine needle aspiration cytology revealed benign lesions in 103 cases and malignant lesions in 126 cases. The Overall results of ultrasound-guided FNA were: sensitivity, 94.5%, specificity, 95.0%, positive predictive value, 96.0%, negative predictive value, 93.2%, accuracy rate, 94.7%, false negative, 5.4%, and false positive, 4.9%. Most specimens (96.4%) were amenable for diagnosis. Conclusion: Fine needle aspiration is a good method for the differential diagnosis of thyroid nodules. High resolution ultrasound-guided FNA with an extension tube is helpful for obtaining good specimens.