To determine if the cochlear implant can enable sound detection in children with a congenitally deformed cochlea, we reviewed warble-tone thresholds in five ears of four children in the implant clinical trials program. Of the five ears, there were two common cavity deformities, two cochlear hypoplasias, and one incomplete partition. Four of the five ears had an auditory response to stimulation by the implant at the same level as ears deafened by other disorders. One ear that had an auditory response to stimulation also produced facial stimulation that precluded use of the implant. The one ear that did not stimulate was the incomplete partition. This ear had a very narrow internal auditory canal. Three patients are now using the implant in three ears to detect sound. Results show that a cochlear implant may enable sound detection in a patient with a malformed cochlea but that a very narrow internal auditory canal (less than 1.5 mm) detected preoperatively on radiographs may contraindicate an implant. Such anatomy suggests only a rudimentary audiovestibular nerve or no such nerve and only a facial nerve.