The endoscopic endonasal approach (EEA) has been reported to be an efficient approach for treating lesions of the petrous apex. However, there have been only limited anatomic studies for the EEA. Furthermore, most of the relevant distances for EEA cannot be measured easily on a cadaveric skull. Two fresh adult cadaver heads and five formalin-fixed adult cadaver heads were dissected using the EEA to identify groups of landmarks for safe guidance during this approach. The distances between these landmarks were then measured by CT angiography by using three-dimensional software. The EEA to the petrous apex can be divided into five phases. In each phase, a group of landmarks, rather than a single landmark, can be identified easily for guiding the next phase of the approach. There was no significant difference between males and females in any of the distances reported in the present study. The EEA can be performed to manage a petrous apex lesion more safely by referring to multiple landmarks and the distances between them. (C) 2012 Published by Elsevier Ltd.