To compare anatomic access to the petrous apex via the nasal and lateral approaches. Hundred consecutive fine-cut CT temporal bones at the Royal Melbourne Hospital from July 27, 2007 to October 30, 2010 were reviewed. Easy lateral access allowed use of a 4 mm burr past vital structures. Easy nasal access was defined as sphenoid pneumatization to/beyond the posterior sella and laterally beyond the maxillary/vidian nerves. Three patients with petrous apex pathology were also reviewed. Easy lateral and nasal access occurred in 74 (37%) and 79 (39.5%) sides, respectively. Easy nasal and lateral access were not strongly correlated (r = 0.10, P = 0.15). A well-pneumatized mastoid (62.5%) was strongly correlated with a large sphenoid (63%, P < 0.001). Pneumatization of the mastoid corresponds to sphenoid sinus size. However, surgical access to the petrous apex is more determined by proximity of vital structures. Easy surgical access via the nasal or lateral approaches was not strongly correlated. Petrous apex lesions requiring surgery should be considered for both approaches. Clin. Anat. 26:682–687, 2013. © 2012 Wiley Periodicals, Inc.