목적: The decision making of thyroid nodule depends on the result of fine needle aspiration cytology (FNAC) or core needle biopsy (CNB). But indeterminate result after FNAC or CNB is inevitable in some proportion and in such cases, repeated biopsy is needed and patient complain about the delay in decision and also increased medical fee. So in this study, the rate of indeterminate result will be compared according to the method of biopsy to find out more appropriate primary work-up modality. 방법:Retrospectively reviewed the biopsy result from 396 nodules from 384 patients. 283 FNA and 219 CNB were performed for these nodules. The rate of inadequate specimen, atypia of undetermined significance (AUS), and follicular lesion of undetermined significance (FLUS) were compared according to the ultrasonographic(USG) finding and the risk stratification system of USG suggested by ATA 2014 guideline 결과:Among 283 FNA, there was 56 inadequate specimen, 68 AUS, 3 FLUS. Among 219 CNB, 4 inadequate specimen, 4 AUS and 40 FLUS were observed. The rate of inadequate specimen and AUS was significantly higher in FNA and FLUS was significantly frequent in CNB. In highly suspicious or intermediate suspicious nodules, 53.2% of FNA returned indeterminate result including 11.3% inadequate, 40.3% AUS, and 1.6% FLUS. CNB resulted in indeterminate result in only 2.7% and showed significantly lower indeterminate result than FNA. In low suspicious nodule, CNB resulted 27.4% of FLUS and failed to show significant difference from FNA. In nodules with very low suspicious or benign feature, FNA was enough for the purpose of decompressing the cystic space. 결론:In highly suspicious or intermediate suspicious nodule, CNB may be more appropriate first modality for the biopsy rather than FNA.