Multielectrode cochlear implantation is the most effective treatment for profound sensorineural hearing loss. In vivo three-dimensional 3-D localization of cochlear implant electrodes is important for modeling of the electrical field in the cochlea, design of electrode arrays, and may improve speech processor programming for better speech recognition. The prerequisite for 3-D localization of the electrodes is their 2-D localization in x-ray radiographs. In this paper, we develop a practical method to localize the electrodes with high efficiency, accuracy, and reproducibility. In this method, a priori knowledge of the electrodes and their approximate positions are utilized, an intelligent thresholding and segmentation mechanism is embedded, and the electrode center is computed as the weighted geometric center of segmented electrode pixels. Experiments with physical phantoms and human data demonstrate the feasibility and utility of this method. The PC-based program developed for this project is disseminated on the Web.