AbstractTwenty‐three patients with primary osteogenic tumors, two osteoblastomas and 21 osteosarcomas, underwent fine‐needle aspiration biopsy in the preoperative investigation. The cytologic features in smears were compared with the light and electron microscopic findings of resin‐embedded fine‐needle aspirates (16 cases) and the histopathologic findings of the surgical specimens. Cytologic smears clearly indicated a primary bone malignancy in all 20 high‐malignancy osteosarcomas. In the osteoblastic osteosarcomas, the diagnosis of osteosarcoma was strongly suggested by the osteoblastic appearance of the tumor cells and the presence of an osteoid‐like fibrillar matrix in 6 of 11 cases in the May‐Grünwald‐Giemsa‐stained smears. The distinction of chondroblastic osteosarcomas from high‐grade chondrosarcomas and of polymorphic osteosarcomas from malignant fibrous histiocytomas is difficult in smears. Electron microscopic examination and immunocytochemistry indicating a positivity for vimentin but not for cytokeratin helped to exclude the possibility of a carcinoma in osteoblastic osteosarcomas where the tumor cells had epithelium‐like features in the smears. The resin‐embedding technique of fine‐needle aspirates was useful for the typing since it gave additional light microscopic information about growth pattern, structure, and matrix production, as well as ultrastructural information about cell and tissue differentiation. The osteoid‐like material seen in May‐Grünwald‐Giemsa‐stained smears could be proven to represent osteoid with varying degrees of calcification at the ultrastructural examination. The fine‐needle aspiration technique, especially when used for both smears and embedding, may play an important role in the preoperative investigation of bone tumors, provided that it is used with full knowledge of t