The cases of deafness presented here have been selected primarily to illustrate the degree to which the acoustic ganglion has degenerated in profound or total deafness. Examples of seven types of acquired diseases of the inner ear and one type of probable congenital degeneration of uncertain cause are given. The number of surviving ganglion cells in each 5-mm section of the cochlea has been expressed as a percentage of the normal average count corresponding to that section of the organ of Corti. The state of the acoustic ganglion has been correlated with that of the organ of Corti and the peripheral axons. Attention is directed to factors other than the presence of ganglion cells, such as disease of the labyrinthine capsule and/or labyrinthitis ossificans, that may influence the possibility of successful insertion of a cochlear implant.