Primary angiosarcoma of bone is a rare neoplasm. The unique cytomorphologic and ultrastructural aspects of a primary angiosarcoma of the cuboid bone diagnosed by fine-needle aspiration are presented. Smears and cell block preparations revealed single and clustered large, pleomorphic, and spindle-shaped cells with a markedly hemorrhagic background. Electron microscopy revealed characteristic features of endothelial cells including rare Weibel-Palade bodies. The clinical, cytologic, histologic, and ultrastructural aspects of the case are discussed.