Abstract: Objective: To evaluate the efficiency of the electrodes of Nucleus CI24M through half year fellow-up observation about the impaired and extra-cochlear electrodes.Methods: 53patients implanted with Nucleus CI24M between June 1998 and August 2002 participated in this study.The impedances of electrodes were measured intra-operatively and at each mapping visits. The impedance test detected the short-or open-circuit electrodes in the arrays.The first detection time of these problem electrodes since surgery were used to calculate the cumulative survival percentage.Postoperative cochlear view radiography at initial stimulation was used to determine part-insertion or full insertion of the electrode array.The influence of surgical procedure and surgeon's implant experiences were analyzed.Results: Percentage of cases with even one impaired electrode was 13.2%； the risk ratio of re-insertion for electrode impairment was 0.4656.Part implantation occurred in 15.1% patients，most of them (7/11) showed cochlea malformation.The cumulative survival percentage after 4 years use was 96.2%.Conclusion: Nucleus CI24M achieves a very high reliability in 1-4 years device use.The re-insertion during the surgery would like to cause the impairment of the electrodes.The cochlea's fibrosis，malformation， and surgeon's implant experience are the main reasons of the part-insertion of the electrode array.