The aim of the present study was to identify cell types in primary culture from malignant and non-malignant effusions. Effusion samples were subjected to cytology and culture. Immunocytochemistry was performed in cytological slides to evaluate malignancy (positivity for malignancy markers) and in culture slides for identification of cell types in growth. A total of 143 effusion samples (pleural n=76; peritoneal n=37; pericardial n=4; and peritoneal lavage n=26) were analyzed. Cell growth was observed in 34.9% of all samples and immunocytochemistry for identification of cell types in culture slides was conclusive in 90% of them. In non-malignant samples (n=28), growth of mesothelial cells, macrophages and of both cell types was identified in 82.14, 10.71 and 7.14%, respectively. In malignant samples (n=17, all carcinomas), growth of malignant epithelial cells and of both malignant epithelial and mesothelial cells was identified in 41.17 and 23.52%, respectively. In the remaining 35.29% of malignant samples, the only cells in growth were mesothelial and/or macrophages instead of malignant epithelial cells. In conclusion, in culture of malignant effusions, mesothelial cells may be simultaneously identified with malignant epithelial cells. Besides, mesothelial cells and macrophages may be the only cells identified in malignant effusion culture. Therefore, a broad panel of cell markers should be used for unmistakable identification of cells in studies of effusion primary culture. The ideal malignant effusion sample to obtain culture of neoplastic cells should be that without the presence of mesothelial cells and macrophages.