Cochlear implants: a review of the literature. One hundred and seventy-five publications on the subject of implantable devices for deafness were reviewed. Eight categories of publications are identified: (i) hearing aid versus cochlear implant; (ii) cochlear implant device versus cochlear implant speech processor, (iii) cochlear implant versus auditory brain stem implant, (iv) speech processor versus hearing aid, (v) postoperative device programming, (vi) outcome for children implanted pre-school, (vii) outcome for adults who become deaf post-puberty, and (viii) outcome for adolescents who are congenitally deaf. Some publications present evidence and others provide opinion. It is very apparent that much more systematic collection of information on implant outcome is needed in a number of areas including the following: (i) long-term outcome of implanted adults; (ii) hearing results and speech production in children and adolescents; and (iii) developmental outcome in children and adolescents who are congenitally deaf and implanted before the onset of the first school year. Future directions for research in this area are also suggested.