Parapneumonic effusions occur in 20 to 40% of patients who are hospitalized with pneumonia. The mortality rate in patients with a parapneumonic effusion is higher than that in patients with pneumonia without a parapneumonic effusion. Some of the excess mortality is due to mismanagement of the parapneumonic effusion. Characteristics of patients that indicate that an invasive procedure will be necessary for its resolution include the following: an effusion occupying more than 50% of the hemithorax or one that is loculated; a positive Gram stain or culture of the pleural fluid; and a purulent pleural fluid that has a pH below 7.20 or a glucose below 60, or has a lactic acid dehydrogenase level of more than three times the upper normal limit for serum. Patients with pneumonia and an effusion of more than minimal size should have a therapeutic thoracentesis. If the fluid cannot be removed with a therapeutic thoracentesis, a chest tube should be inserted and consideration be given to the intrapleural instillation of fibrinolytics. If the loculated effusion persists, the patient should be subjected to video-assisted thoracoscopic surgery, and if the lung cannot be expanded with this procedure, a full thoracotomy with decortication should be performed. The definitive procedure should be performed within 14 d.