Background Cochlear implants aim to regain or improve hearing for people who are deaf or who have so poor hearing that hearing aids have little or no effect. Cochlear implants are small electronic devices. They transmit sound directly to the hearing nerve via electrodes that are placed in the cochlea by a surgical procedure. This technique relies on the hearing nerve still functioning.

This part of the report, Part A, has evaluated the clinical usefulness of cochlear implants in adults who are deaf or severely hard of hearing. Part B of this report has evaluated the cost effectiveness from a Norwegian perspective.

Methods We searched for systematic reviews, randomised controlled studies and prospective controlled studies in international databases in April and June 2006. We assessed and summarised studies that fulfilled our predetermined inclusion criteria.

Results No randomised controlled trials were identified comparing cochlear implants in adults with waiting lists or hearing aids. We included three prospectively controlled studies. One of the included studies compared cochlear implants (46 participants) with waiting list (16 participants) and two of the included studies compared cochlear implants (32 participants) with hearing aid (24 participants). The group given cochlear implants reported better speech recognition and improved quality of life, but had more complications.

All results should be interpreted cautiously because there was only information from nonrandomised studies, few people included in the studies, large variation in reported effect, and serious challenges with selection of participants to the groups.

No studies fulfilling our predetermined inclusion criteria were identified that compared unilateral and bilateral use of cochlear implants.

Conclusion Cochlear implants in adults may help improve speech recognition and quality of life compared to waiting lists and hearing aids. This information is of very low quality, and there is not enough information available regarding type and frequency of complications and side effects.