Radiology has played a pivotal role in the management of patients with pleural effusions. By confirming the presence of an effusion and providing information regarding the size and distribution of fluid, chest radiography greatly facilitates initial diagnostic thoracentesis. Identification of even small effusions is important because these commonly occur and may have clinical significance. The development of improved antibiotics and a wider range of interventional techniques has increased the reliance on the radiologic imaging of pleural disease in order to plan appropriate therapy. The newer imaging modalities of CT and sonography have proved to be particularly valuable in detecting small effusions and demonstrating single or multiple loculations. Additional features, such as the degree to which a pleural process has become organized and whether there is adjacent lung parenchymal disease, are well assessed on CT. Experience with MR has been limited, but preliminary data suggest that it may be a valuable addition and/or alternative to CT.