The most common forms of severe hearing loss and deafness are related to morphological changes in the cochlea. Many individuals with such forms of hearing disorders have received cochlear implants. It has been assumed that preservation of spiral ganglion cells is important for success of cochlear implants. Preservation of ganglion cells is negatively correlated with the duration of the hearing loss. It has, however, not been possible to reveal a relationship between the degree of survival of spiral ganglion cells and performance of cochlear implants. It is important to understand the histopathological changes that follow cochlear implantation. Insertion of cochlear implants may cause trauma to the basilar membrane, the spiral lamina, and the spiral ligament. Rupture of the basilar membrane may occur. Over time, new bone forms at the cochleostomy and along the implant track. Further investigation is necessary to evaluate the causes of variability of behavioral measures of performance.