A 33-year-old woman who was diagnosed as medullary carcinoma by fine needle aspiration of thyroid mass is presented. The smear revealed dispersed pattern and small clusters of cells without follicular or papillary structures. The nuclei were round, oval or spindle shaped and eccentrically located. The cytoplasm was abundant and showed red-stained cytoplasmic granulation and tail-like projection with indistinct border. Clumps of amorphous, light-green material were intermingled with tumor cells.