The purpose of this investigation is to determine the safety and preliminary efficacy of implanting a cochlear implant (CI) in the profoundly deaf ear of an adult with one normal hearing (NH) ear (termed "single-sided deaf" person, or SSD). The potential subjects will have been deafened post-lingually, thus, at one point the now deafened ear did conduct sound from the periphery. The MED-EL CI system will be implanted in ten (10) SSD patients.The long-term goal of this research program is to determine whether the CI, in combination with the NH ear, may provide improved localization ability and better speech understanding in noise, relative to performance before cochlear implantation (i.e., with the NH ear alone). A secondary long-term goal is to determine whether CI stimulation may reduce tinnitus severity, compared to tinnitus experienced prior to cochlear implantation or when the CI is turned off, after implantation.