Occult pneumothorax is pneumothorax identified by computed tomography but not seen on conventional chest radiographs. Twenty-seven occult traumatic pneumothoraces in 26 patients were identified retrospectively at the authors' level I trauma center. Of these, 24 patients survived to discharge or transfer; 2 died of brain injury. Eleven patients were treated immediately with tube thoracostomy (TT) and 13 were observed with interval chest radiography. The authors' data support the conclusion that it is safe to withhold immediate TT in patients who are hemodynamically stable. Close clinical observation and interval chest radiography can identify those patients who require subsequent TT. Prospective study of larger numbers of patients is needed to confirm the safety and cost efficacy of this approach.