The use of serial chest radiographs (CXRs) to evaluate patients with penetrating thoracic trauma is common practice. However, the time interval between these studies and the duration of observation remains uncertain. The purpose of this study was to evaluate whether a noncontrast chest CT is as reliable as a 6-hour CXR for detecting delayed pneumothorax (PTX) after penetrating thoracic trauma. Hemodynamically stable patients with isolated penetrating thoracic trauma were prospectively evaluated with a CXR and a noncontrast chest CT. If there was no PTX or hemothorax, or a finding that did not require immediate intervention, a 6-hour CXR was obtained. Findings were treated as clinically indicated and patients were discharged if all three studies were negative. One hundred eighteen patients were evaluated (89 stab wounds and 29 gunshot wounds). All initial CXRs were negative. CT identified six PTXs and one hemothorax. Two patients required operative intervention. There were no delayed findings on CXR provided the CT was negative. The mean time to CT and before disposition was 19 minutes and 8 hours, respectively, with a potential decrease in charges of $313.32 per patient. The use of serial CXRs provided no additional information that was not available on the initial chest CT, allowing for expedited discharge, decompressing overcrowded emergency areas, and reducing the number of patients leaving before completion of their work-up.