Compare the left and right images. Histologically verified Hashimoto's thyroiditis is demonstrated on the left, while a histologically proven coexisting Hashimoto's thyroiditis and oxyphilic adenoma on the right one. In the case of the tumor, single cells and microfollicles predominate the smears, while in the case of thyroiditis follicular cells are found in more cohesive structures. An even more important difference can be observed analyzing the occurrence of lymphoid cells. As in this example, no or only scattered number of lymphocytes are present on the smear of a Hürthle-cell tumor. The extensive lymphocytic infiltration practically excludes the possibility of a follicular type Hürthle-cell tumor. In these cases, prominent nucleoli are found completely opposite as in usual cases: oxyphilic cells contain large, prominent nucleoli in this Hashimoto's case, while most oxyphilic cells lack prominent nucleoli in this tumorous case. There is a small, but important difference in the sonographic presentation of these two cases. The lesion in question is larger in the case of oxyphilic tumor than in the case of thyroiditis. This size, i.e. the maximal diameter around 30 mm, practically excludes the possibility that this lesion would be a secondary lobule. Naturally, the statement is conversely not true: the small size of a lesion does not exclude the possibility of a tumor. Moreover, in the case of oxyphilic tumor, the presence of a halo sign and perinodular blood flow are strong arguments for the presence of a follicular type tumor in such relatively large nodule. Taking all of the above properties into account, the diagnosis of Hashimoto's thyroiditis presented in left images was not difficult. In the right case, the combination of cytological and sonographic data led to the correct diagnosis.