Aneurysmal bone cyst (ABC) is an osseous mass lesion that accounts for 1% of primary bone tumors. We describe 23 cases of ABC initially evaluated by fine-needle aspiration biopsy (FNAB). In 4 cases, the ABC was secondary to another primary tumor. Aspirates from 6 cases (26%) were insufficient. Twelve aspirates diagnosed as ABC by FNAB were confirmed as ABC by histologic examination. The accuracy of FNAB was 82% when cases insufficient for evaluation were excluded. One case diagnosed as ABC cytologically was subsequently found to be metastatic carcinoma. In another, the specimen was interpreted as ABC vs giant cell tumor. In the remainder, a diagnosis of ABC was favored cytologically. Owing to the nonspecific findings, ABC cannot be definitively diagnosed by FNAB. However, the presence of typical clinical and radiographic features in conjunction with a blood-rich, mesenchymal cell containing aspirate devoid of overtly malignant cells strongly suggests the diagnosis of ABC.