Marginal vacuoles (MV) found in Giemsa‐stained fine‐needle aspirates of the thyroid gland have been observed in toxic and also in non‐toxic goiters. The aim of our retrospective study was to disclose the incidence and diagnostic significance of MV in 46 smears from 43 patients with primary and/or metastatic follicular thyroid carcinoma (FTC). Typical MV, MV‐like structures, or both were found in 14 of 36 specimens (39%) of the primary tumor and in four of seven specimens (57%) obtained from metastases of FTC. No association between the appearance of MV/MV‐like structures and degree of tumor differentiation was demonstrated. On the other hand, MV or/and MV‐like structures were more frequently (69%) documented in hyperthyroid patients (P < 0.05). Accordingly, our study demonstrated relatively frequent appearance of MV or MV‐like structures in FTC independent of tumor differentiation. Their appearance, however, seems to be associated with hyperthyroidism. Diagn Cytopathol 1996;15:93–97. © 1996 Wiley‐Liss, Inc.