A mediastinal mass was aspirated by fluoroscope-guided fine needle aspiration biopsy in a 47 years old female patient. The first aspiration smears were not diagnostic, because of hemorrhagic background and cell paucity. On the second aspiration, the smears were composed of some clusters of benign epithelial cells in hemorrhagic back-ground. Cells were arranged in mostly solid sheets and tended to form glandular lumina in part. Their nuclei were round and vesicular. Nucleoli were not prominent. These findings were suggestive of benign glandular tissue, which was finally confirmed as mediastinal thyroid gland by open thoracotomy specimen.