RESUMEN
Anaplastic carcinoma of the thyroid is one of the most malignant tumors and survival for longer than three years after diagnosis is exceptional. Multinucleated giant cells of osteoclastlike appearances are seen in some of the anaplastic carcinoma, but only three cases in which the diagnosis was made by fine needle aspiration(FNA) cytology are reported in the international literature. We experienced a case of anaplastic carcinoma with osteoclastlike giant cells in a 66-yr-old female, diagnosed by FNA cytology. The smears revealed two cell populations; multinucleated giant cells and large polygonal or spindle shaped malignant cells. The FNA cytodiagnosis of anaplastic thyroid carcinoma containing osteoclastilke giant cells was substantiated by subsequent biopsy.