Objective: The challenge in diagnosis of effusion is in differentiation of reactive and neoplastic mesothelial or metastatic cells and identification of primary neoplasia. The difficulties in this differential diagnosis derived from the low sensitivity (~50 %) and specificity of effusion cytology. By identification of tumor associated aneuploidy FISH could enhance the cytodiagnostic yield in effusions. Method: We used Urovysion™ (Abbott), a FISH commercial kit, designed for identifications of Ch. 3, 7, 17 polisomy and 9p21 loss in urothelial tumors. It has been applied to detect chromosomal aneuploidies as a marker of malignancy in 64 effusions with or without known source primary tumors. Also was evaluated reproducibility of molecular alterations with primary tumors and any their specific aneuploidies. Results: FISH positivity was observed in 44 (69 %) of cases, whereas 31 were positive at cytology (48 %). Overall results of cytology and FISH together rised to 75 %. Conclusion: Urovysion™ test could be an useful tool to distinguish malignant cells in inconclusive effusions cytology but it doesn't seem to be used to provide definitive indications about primary neoplasia.