Chondroblastoma of bone is a well-characterized entity. When the radiographic features are classic and the lesion is present in typical locations (i.e., epiphysis of a long bone), the diagnosis is often easily established by fine-needle aspiration biopsy and/or surgical curettage. Tumors in unusual locations, in older patients, or when complicated by aneurysmal bone cysts may pose more diagnostic diffΔ±culty. We report four examples (three primary and one recurrent) of chondroblastoma of bone diagnosed by fine-needle aspiration biopsy. All patients were men, ranging from 18 to 28 yr of age. Sites of involvement included the acromion process of the scapula, left humerus, right ischium, and left distal femur. Three of the tumors were diagnosed as chondroblastoma on fine-needle aspiration cytology; the fourth case, involving the scapula, consisted mostly of a large aneurysmal bone cyst and remained unrecognized until surgical curettage was performed. Typical-appearing chondroblasts were present in three of the cases; osteoclast-type giant cells were observed in all four cases. Matrix material consistent with chondroid was also identified in all cases. We believe that in the absence of inflammatory cells, the presence of classic-appearing chondroblasts, even without chondroid matrix, is suffΔ±cient for a diagnosis of chondroblastoma of bone. Diagn.