Inclusion Criteria:

* Sixty-five years of age or older at the time of the study and CMS-eligible as primary source of medical insurance coverage.
* Bilateral moderate to profound hearing loss in the low frequencies (up to 1000 Hz) and profound sensorineural hearing loss in the high frequencies (3000 Hz and above).
* Preoperative aided sentence score in quiet greater than or equal to 40% correct but less than or equal to 60% correct in the best aided condition on recorded AzBio sentences.
* English spoken as the primary language.

Exclusion Criteria:

* Congenital hearing loss (for the purpose of this study, onset pror to 2 years-of-age).
* Preoperative aided sentence score less than 40% or greater than 60% correct in the best aided condition on AzBio sentences in quiet
* Ossification, absence of cochlear development or any other cochlear anomaly that might prevent complete insertion of the electrode array.
* 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.
* The audiologist and/or surgeon will review the study protocol with the patient prior to having him/her sign the consent form. If the patient indicates he/she is unwilling or unable to comply with all investigational requirements, he/she will not be enrolled in the study.
* Using best clinical judgment based on professional interaction with the patient and his/her family, the managing audiologist and surgeon will determine if there are any disabling cognitive limitations that would prevent the patient from providing reliable data for this study.