Dermoid cysts account for less than 1% of all intracranial neoplasms and these are principally situated close to the midline. Those located at the petrous apex are generally in the intradural, and less frequently in the interdural, compartment. We report a 37-year-old woman with a giant interdural dermoid cyst of the petrous apex, associated with erosion of the middle fossa floor, and review the relationships of these dysembryogenic lesions, the dura mater and the neurovascular structures of this complex anatomical region, along with the relevant literature.