Introduction The prevalence of thyroid nodules is 4-7% in adults. Although less than 5% of nodules in adults are malignant, most nodules are non-neoplastic or benign. Fine needle aspiration (FNA) is a diagnostic technique for evaluation of non-toxic nodules, which has been widely accepted. Its primary objective is the patient triage in order to identify those who need surgery and aid in the decision of the appropriate surgical procedures. Materials and Methods This retrospective study was

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... ted on 116 patients who underwent thyroidectomy in Semnan's Kowsar Hospital during 2011-2018 in Iran. The data were recorded before and after the surgery in the checklist. The data were compared and the sensitivity, specificity and diagnostic accuracy of FNA were calculated. Data were analyzed by SPSS software (version 18.0) and analyzed by Chi-Square test and Independent Samples test. Results The sensitivity of FNA was 96.9%; its specificity was 81.7%; its positive predictive value (PPV) was 73.8%; its negative predictive value (NPV) was 98%; and its diagnostic accuracy was 86.9%. For the nodules smaller than 4 cm, FNA was calculated with higher sensitivity, specificity, PPV, NPV, and diagnostic accuracy compared to nodules larger than 4 cm. Conclusion FNA is a reliable screening method for preoperative assessment that can accurately detect malignant cases from benign cases, especially if the size of the nodule is smaller than 4 cm.