Although subacute granulomatous thyroiditis(SGT) is usually diagnosed clinically, papillary carcinoma or other thyroid conditions must be considered in the differential diagnosis. We retrospectively reviewed the clinical and fine-needle aspiration(FNA) cytologic findings seen in 10 SGT cases to decide what are the most reliable cytologic findings and the most helpful molecular tools for reaching a confident cytologic diagnosis. The most representative smear slides were retrieved to perform immunocytochemistry for cytokeratin19(CK19) and Ret protein. Five papillary carcinomas(PTCs) were included as controls. The constant and typical cytologic findings of SGT were multinucleated giant cells(MGCs) (100%), epithelioid granulomas(90%), an inflammatory dirty background(90%) and plump transformed follicular cells(80%) without fire-flare cells, oncocytic cells or transformed lymphocytes. The immunoreactivities for CK19(37.5%) and Ret(10%) of the follicular cells of SGT were less than those(CK19 and Ret:100%) of PTC. CK19 immunoreactivity of the MGCs was seen in only one case of PTC. There was no significant difference between CK19 and Ret immunocytochemical staining for the MGCs of both SGT and PTC. The results of this study demonstrate that the cytological diagnosis of SGT can be improved by employing a combination of the typical and constant diagnostic cytological features and immunocytochemical results.