Access to the inner ear, specifically the cochlea, is required for cochlear implant (CI) surgery, in which an electrode array is used to stimulate the auditory nerve and allow deaf people to hear. More than 240,000 CIs have been placed worldwide with approximately 70,000 performed in the USA. Projections indicate that up to 750,000 Americans with severe hearing loss may benefit from CI. In our ongoing NIH-funded project (R01 DC008408), we have demonstrated the feasibility of percutaneous cochlear implantation (PCI). PCI reduces CI surgery to a single pass of a drill from the lateral skull surface to the cochlea. The drill path is planned and executed using image-guided technology so as to avoid vital adjacent anatomy (e.g. the facial nerve) and hit the target-the scala tympani of the cochlea. In clinical trials we have validated the PCI technique on 31 adult patients with statistical projections indicating avoidance of vital anatomy at a rate similar to that of traditioal surgery. Furthermore, we have begun implementation of PCI by developing instruments and techniques for drilling and have performed incrementally deeper drilling on 10 additional patients the most recent of which had complete PCI performed. The potential benefits of PCI are many including less tissue removal and shorter time of surgical intervention. In the attached submission, we propose to build on our successful development of PCI and explore potential benefits by (i) extending our Phase I study by one year in order to produce a robust clinical protocol and (ii) carrying out a Phase II study consisting of a randomized clinical trial comparing PCI to traditional CI surgery. More specifically, during Phase I we will (a) further refine our imaging and planning software to optimize accuracy and usability, (b) implement redundant safety checks to minimize risk of injury to the facial nerve, (c) investigate three options for creating the opening into the cochlea via the PCI track and picking the best one for the final protocol, (d) investigate the use of endoscopes for verification of accurate targeting of the scala tympani component of the cochlea, and (e) finalize design of an insertion tool for final CI electrode placement. In the Phase II randomized trial we will compare, head-to-head, traditional CI and PCI surgery with formal endpoints being (a) amount of tissue resected during intervention and (b) time of intervention. These formal metrics will be used to assess (a) the impact of the procedure on individual patients, which may portend quicker recovery and quicker CI activation for PCI patients, and (b) the overall cost of intervention which despite the need for additional equipment may be cheaper for PCI due to decreased operative time. While our study is set up to demonstrate statistically significant reductions in both volume of tissue removed and time of intervention, we will remain open to other potential benefits (e.g. more consistent electrode placement in the scala tympani with PCI). If our study is successful, we posit that PCI will become the preferred technique for CI.