Cytological examination is a valuable diagnostic tool in case of a serous effusion. The first manifestation of malignancy may be an effusion of the pleural, pericardial, or peritoneal cavity, especially in carcinoma of the ovary, or lung, and malignant mesothelioma. In other malignancies effusions may occur in the course of the disease. The contribution by Mother by et al. in this issue of ACP ...