Pulmonary effusion in the elderly generally refers to pleural effusion in the elderly, implying that the elderly may have cardiac insufficiency, lung malignancy, pneumonia, tuberculosis, malnutrition and other diseases. 1. Cardiac insufficiency: diseases such as coronary heart disease, chronic pulmonary heart disease, degenerative changes of heart valves, constrictive pericarditis and so on can cause cardiac insufficiency leading to pleural effusion in the elderly. 2. Malignant tumor of lung: the incidence of malignant tumor is high in the elderly, and malignant tumor or metastatic tumor of lung and pleura can stimulate the pleura and cause pleural effusion. 3. Pneumonia, tuberculosis: the elderly body resistance is reduced, easily infected with pneumonia or tuberculosis, causing pleural effusion. 4. Malnutrition: poor appetite and gastrointestinal malabsorption of the elderly can lead to malnutrition and hypoproteinemia, which can cause pleural effusion. Other causes of pleural effusion in the elderly include liver and kidney diseases, rheumatologic and immunologic diseases, etc. It is recommended to go to the hospital for further examination and treatment.