We report a rare case of a 78-year-old woman with anaplastic carcinoma of the thyroid diagnosed by fine needle aspiration cytology. Cytological tumor features included many dispersed fusiform cells, a high N/C ratio, and oval nuclei with few nucleoli. Many tumor cells had hemosiderin granules in the cytoplasm. Granules were also observed in the resected thyroid tissue with Prussian blue stain. In cytologic examination of the thyroid anaplastic carcinoma, it is important to differentiate between tumor cells containing hemosiderin granules and cells of benign cystic change lesions.