The cytologic findings observed in fine needle aspiration (FNA) biopsy smears from 27 cases of renal tumors in children are reported. The aspirates were from 16 cases of classical Wilms' tumor (WT), one anaplastic WT, 2 clear cell sarcomas of the kidney (CCSK), 2 malignant rhabdoid tumors of the kidney (MRTK) and 6 congenital mesoblastic nephromas (CMNs). The stromal component was present in 16 of the 17 cases (94%) of WT, and the epithelial component in 13 of the cases (76%). Blastema was noted in all 17 cases of WTs. Necrosis was present in 11 (65%) of the smears from WTs. Other features identified include tubular and glomerular differentiation (6 cases), rosette formation (2 cases), striated muscle differentiation (one case) and anaplasia (one case). Smears from malignant rhabdoid tumors of the kidney (MRTK) tended to be very cellular, comprizing cells with prominent esinophilic nucleoli. Cells from clear cell sarcoma of the kidney (CCSK) were usually arranged in smaller discrete groups with fragile cytoplasm. In congenital mesoblastic nephroma (CMN), the cells tend to be spindly and very cohesive. A definite tumor type was able to be made on 25 of the 27 cases (93%) of renal tumors.