OBJECTIVE To compare the diagnostic sensitivity and specificity of fine needle aspiration (FNA) to those of needle core biopsy (NCB) and to attempt to determine if a complementary role exists for the two modalities. METHODS Skeletal lesions in 144 patients were evaluated with concomitant FNA and NCB over a 21-year period. FNAs and NCBs were divided as diagnostic of neoplasm, normal or inflammatory (i.e., osteomyelitis), or unsatisfactory. The results of each modality were then reviewed and compared. RESULTS In the 144 total cases, a diagnosis was possible in 79% (114) cases. FNA and NCB concurred in 73% (83) of diagnostic cases. Concurrence was 87% between diagnostic FNA (83) and NCB (95). The two modalities agreed in 78% of cases diagnosed as metastatic carcinoma and in 59% of primary malignant tumors of bone (17) (excluding Ewing's sarcoma). FNA alone was diagnostic in 8% (9) of cases, including 5 metastatic carcinomas, 2 chondrosarcomas, 1 Ewing's sarcoma and 1 case of osteomyelitis. This represented 24% of the 38 cases in which NCB was unsatisfactory (11) or normal (27). NCB alone was diagnostic in 19% (22) of cases, including 11 metastatic carcinomas, 3 osteosarcomas, 1 chondrosarcoma, 1 spindle cell sarcoma (not otherwise specified), 1 Ewing's sarcoma, 2 capillary hemangiomas and 3 cases of osteomyelitis. This represented 43% of the 51 cases in which FNA was misinterpreted (2), unsatisfactory (33) or normal (16). NCB more specifically typed a metastatic lesion or suggested a primary focus in 21% (12) of the 58 cases in agreement. It also more specifically subtyped 50% (5) of the 10 primary malignant tumors of bone. CONCLUSIONS Given these findings, NCB is more specific in the evaluation, grading and typing of skeletal lesions in particular malignant primary bone tumors. Overall, there is excellent agreement between FNA and NCB, especially in the evaluation of benign primary bone tumors. Most important, FNA improved the diagnostic yield in 24% of cases when NCB was normal or unsatisfactory, obviating the need for rebiopsy. FNA should be performed concurrently with NCB in the evaluation of skeletal lesions since the two modalities are complementary.