The vast majority of thoracic trauma victims require only observation or tube thoracostomy for definitive treatment of their thoracic injury. Although tube thoracostomy is generally considered a limited intervention, 2 to 25 percent of patients who undergo this procedure develop infectious complications. To determine the incidence and risk factors for the development of empyema thoracis after tube thoracostomy, a retrospective study was undertaken. We found that the development of empyema thoracis was increased in patients whose pleural space was incompletely drained and whose thoracic catheters were in place for a prolonged period.