The impact of specialized training in critical care producing a heightened index of suspicion for the diagnosis of pneumothorax in intensive care unit (ICU) patients was prospectively examined. During a 12-month period, 28 ICU patients were found to have a pneumothorax. Nine of the 28 patients with pneumothorax (32%) were initially misdiagnosed by physicians who neither received specialized training in critical care nor routinely cared for critically ill patients. Six of these nine initially misdiagnosed pneumothoraces (67%) were correctly diagnosed by a physician with specialized training and experience in critical care medicine prior to any clinical deterioration in the condition of the patients. This study suggests that specialized training and experience in the management of critically ill patients can significantly improve upon the diagnosis of pneumothorax in these patients and limit the occurrence of tension pneumothorax in the same patient population.