The use of fine-needle aspiration biopsy (FNAB) in the initial evaluation of pediatric bone and soft tissue tumors is controversial, especially for those patients being considered for histiogenetic-specific therapeutic protocols, e.g., the Intergroup Rhabdomyosarcoma Study Group, the Pediatric Oncology Group. We retrospectively reviewed 33 consecutive FNAB specimens (28 primary tumors, 5 metastases) from 32 pediatric patients (< or = 19 yr of age), none of whom had a previously established tumor diagnosis. In one patient, FNAB of the primary tumor and a presumed axillary metastasis were obtained concomitantly. The cytomorphologic analysis included osteosarcoma, eight patients; rhabdomyosarcoma, five; neuroblastoma, five; Ewing's sarcoma/primitive neuroectodermal tumor, four; Langerhans' cell histiocytosis, three; and one each synovial sarcoma, undifferentiated sarcoma, infantile myofibromatosis, fibroma, chondroblastoma, chondromyxoid fibroma, and desmoplastic small round-cell tumor. Ancillary studies, e.g., immunocytochemical analysis, were used in 13 cases. Cytogenetic analysis helped to confirm one Ewing's sarcoma [t (11;22) (q24;q12)] and one synovial sarcoma [t(X;18) (p11;q11)]. With adequate FNAB specimens, a histogenetic-specific diagnosis was rendered in 27 (93%) of 29 cases, and all were correctly recognized as either benign or malignant. One case each of Langerhans' cell histiocytosis, chondroblastoma, and infantile myofibromatosis yielded unsatisfactory specimens. Fibroma and desmoplastic small round-cell tumor were initially misclassified as nodular fasciitis and rhabdomyosarcoma, respectively. Of 18 patients clinically eligible for histogenetic-specific therapy protocols, an accurate diagnosis was obtained in 17 patients. With a multidisciplinary approach and judicious use of ancillary studies, FNAB represents a highly accurate and cost-effective technique for the diagnosis of pediatric bone and soft tissue tumors, especially sarcomas, and should be considered as a viable diagnostic technique for pediatric therapeutic protocols.