A retrospective review was made of 500 consecutive thin-section axial CT scans of the adult sphenoid sinus using contrast enhancement and the bone algorithm to determine whether there was exposure of the cavernous sinus and the carotid arteries along their parasphenoidal course. At least one cavernous-carotid complex that could be considered at risk during sphenoid sinus surgery was seen in 31.4% of the patients. Of this group, 14.4% of the patients had no bony covering on one or both sides at some point along the parasphenoidal course. In 17% the bony covering was so thin it would give minimal, if any, protection from surgical trauma. A patient who had laceration of an unprotected carotid artery with development of post-traumatic aneurysm is discussed.