Endoscopic endonasal surgery (EES) provides direct access to the clivus from the posterior clinoids to the foramen magnum. Tumors such as chordomas and chondrosarcomas are ideally suited for EES due to their central location and infiltration of bone. The most important prognostic factor following surgery is the ability to achieve a gross total resection. There is a significant learning curve associated with clival surgery, especially with the ability to achieve a gross total resection. Effective surgery of the clivus and neighboring regions requires thorough knowledge of the anatomy. The clivus is divided into three regions, each with its own associated vessel and cranial nerve. Access to the clivus is limited superiorly by the pituitary gland and the internal carotid arteries laterally. Anatomical dissections will be used to highlight anatomical landmarks and anatomical relationships. Surgical techniques of EES of the clivus and petrous apex will be demonstrated using case examples with surgical videos. Pituitary transposition provides access to the superior clivus. The contralateral transmaxillary approach is a new approach that maximizes access to the petrous apex deep to the paraclival and petrous segments of the internal carotid artery. Clival defects are difficult to reconstruct and have a higher risk of postoperative cerebrospinal fluid leaks. Specific clival reconstructive techniques will be demonstrated for primary and secondary reconstruction along with data regarding the use of lumbar spinal drains. Learning Objectives: 1.Identify key surgical landmarks for surgery of the clivus and petrous apex. 2. Implement safe and effective surgical techniques for the endoscopic resection of tumors of the clivus and the petrous apex including clival chordoma, cholesterol granulomas and chondrosarcomas. 3. Optimize reconstructive options for large posterior fossa defects including the use of lumbar drainage. Faculty: Audrey Erman, MD(Nothng to disclose), Steven J. Wang, MD(Nothing to disclose).