To evaluate the incidence of facial nerve stimulation from cochlear implants and to better define the segment of nerve being stimulated and the causes of stimulation. Retrospective patient case review and a temporal bone dissection study. A tertiary care setting. All patients given a cochlear implant at the Hospital of the University of Pennsylvania. This encompassed only adult patients. All patients had surgical insertion of either a 3M single channel, Nucleus 22-channel, or CLARION multichannel cochlear implant. Demonstration of facial nerve stimulation with a cochlear implant and determination of affected electrodes; measurement of electrode location and distances between the labyrinthine segment of the facial nerve and the cochlea in temporal bone dissections: and determination of the relationship between the labyrinthine facial nerve and the cochlea using computed tomography evaluation. The overall incidence of facial nerve stimulation using all three devices was 14% (8 of 58). Otosclerosis and otosyphilis appear to be predisposing conditions to stimulation. The mid-cochlear electrodes, located near the labyrinthine facial nerve, appear to cause stimulation of the VIIth nerve most commonly. Computed tomographic evaluation of the bone between the labyrinthine fallopian canal and the cochlea may provide some indication of potential facial nerve problems. Facial nerve stimulation from the use of cochlear implants is more prevalent in patients with otosclerosis and otosyphilis. The labyrinthine segment of the facial nerve is the most likely area being stimulated in most patients. Preoperative computed tomographic evaluation may be beneficial in determining the possibility of this problem.