Barotraumatic cerebral air embolism is described as sudden loss of consciousness accompanied by major motor disturbances. However, arterial gas embolism can have disturbances of cortical function that are much more subtle. Four patients presented with significant abnormalities of mental status. In two patients, the findings were subtle enough that the patients were initially regarded as normal. In the other two, cortical dysfunction was relatively resistant to therapy and might have gone unrecognized without careful examination. In order to detect disturbances in cortical function the neurologic examination should include testing beyond the usual emergency evaluation of consciousness and degree of orientation.