Conclusion. The modified round window insertion enables reproducible insertion into the scala tympani as demonstrated by comparing the 64-CT scanning data and the surgeon's reports. Objective. To estimate the postoperative cochlear implant electrode position using a modified round window approach. Patients and methods. In a prospective study, 82 patients were operated via a modified round window approach to insert primarily into the scala tympani. Surgery had been performed from 2005 to 2008, implanting a Nucleus Freedom RECA device (Cochlear Corp.) (n=43) or 90 k Helix device (Advanced Bionics Corp.) (n=39). The array localization within the cochlea was determined by axial scanning overview, digital reconstruction of a 64-slice CT and by evaluation of the surgeon's report. Results. In 78 (95.1%) patients, the array could be located in the scala tympani. In four cases, the position of the electrode was changed intracochlearly from the scala tympani to the scala vestibuli. In three additional cases, the scala vestibuli was inserted intentionally because the tympanic scale was found to be obstructed intraoperatively due to ossification. There were no significant differences between the intraoperative positioning and postoperative localization of the electrode arrays of the two manufacturers.