Pneumothorax in the ED most often will be primary and spontaneous in a young person who may be treated with either chest tube, mini-chest tube, or aspiration of pneumothorax according to local preference. The other large group of pneumothoraces will be spontaneous but secondary to a disease process, procedure, or drug abuse. The treatment of these must be individualized because conservative measures may not work and the underlying process may require attention as well. Although gaining in popularity, the use of devices or procedures other than formal chest tubes is still not general practice. The major complication of pneumothorax is tension pneumothorax, which is rapidly fatal and must be excluded immediately in all patients regardless of the etiology. Treatment of this complication must be carried out without delay for further diagnostic studies by venting the chest. The significance of pleural effusion depends on its volume and composition. If the cause is not known with certainty or if the patient is dyspneic, thoracentesis should be performed. The fluid is sent for numerous tests including specific gravity, pH, glucose, LDH, and protein. On this basis it is determined as either transudate, which tends to be associated with more benign disorders, or exudate, which is seen with infection, malignancy, and numerous other processes. In all cases the underlying disease requires therapy but only certain exudates require aggressive treatment primarily. Many parapneumonic effusions and all empyemas are exudates that require tube thoracostomy.