Malignant pleural effusions are the major cause of pleural effusions in patients older than 40. Their treatment is essentially palliative but recently improved with new efficient chemotherapy. The most frequent causes of malignant pleural effusions are pleural metastatic adenocarcinomas arising from lung in both sex, or from breast in women, and malignant mesothelioma. In both cases, thoracoscopy is useful for histological biopsies and sclerotherapy by talc poudrage. Pleural malignant mesotheliomas are linked in 70% of cases to professional asbestosis exposure. The histological diagnosis is difficult, relying on a standardized immunohistochemical analysis. Prophylactic irradiation has been proved to be efficient in the prevention of parietal seeding along the thoracocentesis and drainage channels. PET imaging could be of major interest in the diagnosis of mesothelioma and prognosis evaluation. Mesothelioma prognosis has recently been modified by the association of cisplatin with pemetrexed, a new antimetabolite agent, but mesothelioma remains seldom curable.