목적: The aim of this study is to evaluate the factor of false positive by fine needle aspiration (FNAC) cytology. 방법:This study retrospectively reviewed the cytopathological reports of 23402 patients that underwent thyroidectomy based on a diagnosis of PTC by FNA between February 2011 and October 2014. This study re-evaluated the cytology and histopathology of the patients that received false positive diagnoses of PTC by FNAC. 결과:49 patients received false positive diagnoses of PTC by FNAC. 19 case are thyroiditis in permanent result. 12 patients had thyroid disease past history (4 case hyperthyroidism, 7 case hypothyroidism, 1 case Graves disease). 결론:Thyroiditis or thyroid disease past history should be considered possibility of false positive result of FNAC.