Thoracic computed tomography (CT) was performed on 19 ICU patients to define chest abnormalities not clearly seen on conventional portable chest radiographs. In five (26%) of these cases, the CT demonstrated new findings that substantially altered the patient's course including malpositioned thoracostomy tubes, loculated pleural fluid, unsuspected pneumothorax, and pericardial effusion. In selected cases, thoracic CT can provide precise definition of intrathoracic problems in the critically ill patient.