Pleural fluid eosinophilia is rare and is commonly considered as an indicator of good prognosis. In a series of 224 patients, pleural eosinophilia was present in four of 84 malignant cases; however, the incidence of malignancy in the presence of pleural eosinophilia was 0.40, being explained by a relatively high prevalence of malignancies in the population studied. Although pleural eosinophilia is rare in malignant effusions, it cannot be considered as indicating a good prognosis without taking into consideration the local prevalence of malignancies.