Recurrent malignant effusions present a difficult management problem and are a major cause of morbidity. This article reviews the pathophysiology of serosal effusions, with particular reference to those occurring in malignant diseases. A detailed review of the investigations available and the characteristic findings in malignant effusions is presented. The influence of serosal cavity fluid dynamics on the pharmacology of intracavitary chemotherapy is discussed, and a rational approach to intracavitary treatment is presented. The treatment options for patients with malignant effusions are described and the present status of medical treatment is discussed.