The conventional cytology rate for identification of neoplastic cells in effusions is about 60%. The rate of diagnostically equivocal effusions in routine cytology is dependent on the volume of effusion examined, type of preparation and staining, experience of the examiner, and application of ancillary methods. The aim of our study was to confirm the role of image cytometry analysis (DNA-ploidy) on pleural effusions. In this retrospective study based on 42 available cases with a histological diagnosis, we have examined 13 reactive mesothelial proliferations and 29 cases of malignant tumors (adenocarcinoma [ACA] or mesothelioma). The smears collected were submitted to the image analysis following a-three step protocol (smears stained with the Papanicolaou method were destained and then restained with Feulgen staining and finally analysed using image analysis cytometry). The results have shown that nonmalignant cases (reactive mesothelial proliferation) were all diploid and in contrast all aneuploid cases corresponded to malignant tumors. Only three mesotheliomas showed a diploid profile. In conclusion, these results confirm data from literature and indicate that cytometric analysis of nuclear content is a useful marker for identification of malignant cells in equivocal effusions and can be used to increase the cytological sensitivity in doubtful mesothelial proliferations