Pleural effusion refers to the imbalance between the production and absorption of pleural fluid, where the amount of fluid produced exceeds the amount of fluid absorbed, causing the amount of fluid in the pleural cavity to exceed the normal level. It can be a passive leakage or an active exudation process. Pleural effusion in the elderly is a very common clinical syndrome, which can be caused by lesions of the pleura itself or by systemic diseases. It often coexists with other diseases, and the onset is often insidious, with atypical symptoms, which can easily delay diagnosis and treatment. For elderly patients with pleural effusion, it is certainly important to remove the effusion and relieve lung compression, but active treatment of the cause and primary disease is more important. Pleurisy is an inflammation of the pleura caused by various reasons, and it is one of the main causes of pleural effusion.