At switch-on (first post-operative stimulation of the implant) and during subsequent reprogramming, electrodes can, in some patients, be found to be non-functional or to be performing sub-optimally for a number of reasons. This paper examines the reasons for the poor performance of these electrodes by means of a retrospective analysis of 100 patient records. All of these patients received the Nucleus multichannel device. The most common reason for an electrode to require de-activation was found to be facial nerve stimulation, with poor sound quality and pain also being very common. Other reasons included absence of auditory stimulation, vibration, reduced dynamic range, throat sensations, absence of loudness growth or dizziness. The occurrence of these reasons along the electrode array was examined, more basal electrodes being found to be non-functional as a result of having a small dynamic range or poor sound quality. Pain and vibration were found to occur throughout the array and the more apical electrodes were found to be non-functional as a result of facial nerve stimulation. It is suggested that the electrodes at the basal end of the array are likely to be extra-cochlear or are at the site of the most cochlear damage, whereas the more apical electrodes lie in closer proximity to the facial nerve.