Needle thoracostomy is an emergency procedure used to both diagnose and initially treat a tension pneumothorax. We report a case of fatal tension pneumothorax in an intubated patient with chronic obstructive pulmonary disease that was missed by this technique. A tension pneumothorax involving only the right middle and lower lobes was found at autopsy. The autopsy also suggested that needle thoracostomy was misleading because it sampled air from a noncommunicating bulla in the right upper lobe rather than from the pleural space. Tension physiology can exist with only localized collapse of a lung, and diagnostic needle thoracostomy can be falsely negative. When tension pneumothorax is strongly suspected, if empiric thoracentesis does not vent air under pressure, subsequent tube thoracostomy is indicated.