Clinical Evaluation of the Nucleus 5 Cochlear Implant (CI) System

Inclusion Criteria: * Eighteen years of age or older at the time of the study. * Postlinguistic onset of bilateral severe-to-profound sensorineural hearing loss * Bilateral severe-to-profound hearing loss that meets current cochlear implant criteria (\<50% open-set sentence recognition in quiet scores in the ear to be implanted and \<60% in the best-aided condition) * English spoken as the primary language. * Willingness to participate in and to comply with all requirements of the study * Subject may receive bilateral simultaneous cochlear implants. Exclusion Criteria: * Previous cochlear implant experience * Congenital hearing loss (for the purpose of this study, onset prior to 2 years-of-age). * Ossification, absence of cochlear development or any other cochlear anomaly that might prevent complete insertion of the electrode array. * Normal hearing in one or both ears. * Hearing loss of neural or central origin (e.g., deafness due to lesions on the acoustic nerve or central auditory pathway). * Active middle-ear infection. * Unwillingness and/or inability of the candidate to comply with all investigational requirements including, but not limited to, study protocol and surgical procedure.