A typical patient with pneumothorax correctly diagnosed by US and missed by CXR. This 42 year old male patient sustained injuries from a car accident, and arrived with dyspnea, tachycardia, hypotension and desaturation requiring mechanical ventilation. (a) The supine chest radiograph did not enable a diagnosis of pneumothorax. (b) A rapid exploration of the thorax by US indicated medium left pneumothorax (absence of lung-sliding), associated with left lung contusion and pleural effusion. (c) The diagnosis was confirmed afterwards by chest CT. Arterial oxygenation was improved after chest tube placement.