This chapter describes surgical assistance using artificial intelligence (AI) and extended reality (XR). AI technology can now analyze various data and is gaining ground in the medical field. XR technology enables the integration of virtual environments with the real world. Computer-aided surgery (CAS) systems can be enhanced by combining these technologies. A surgical navigation system is a typical CAS system using AI and XR. This system provides surgical assistance information about the anatomical structures in the operative field by fusing the real and virtual environments. In this chapter, we focus on surgical navigation systems using AI and XR and present our surgical navigation systems based on virtual endoscopy systems and their clinical applications.