Fine-needle aspiration (FNA) followed by a core-needle biopsy during general anesthesia is a method for diagnosing pediatric tumors in our Institute. To complete the diagnosis in the case of round cell sarcomas, cytology material is also used for genomic analyses, that is, karyotyping and molecular biology-derived techniques. Fifty primary Ewing sarcomas/peripheral neuroectodermal tumors (ES/PNET) in 50 patients were sampled. Cytological diagnoses were “malignant” in all cases and accurate (ES/PNET) in 46 (92%). Two (4%) cases were misdiagnosed as neuroblastoma, and two others (4%) as rhabdomyosarcoma and nephroblastoma. No suspicious or false-negative results were rendered. Karyotyping was performed in 20 (40%) cases and was interpretable in 17 cases but not in three cases. Molecular search for ES/PNET fusion transcripts were performed in all cases and were detected in 44 (88%) cases, but not in six (12%) cases. In conclusion, FNA assisted by genomic techniques is powerful methods to accurate diagnose ES/PNET. Diagn. Cytopathol. 2012. © 2010 Wiley Periodicals, Inc.