Choice of the side for cochlear implantation should take into account peripheral (extracortical) factors and central (cerebral dominance) factors. From 111 patients implanted with a Nucleus device, the authors found that significant peripheral factors were the degree of cochlear ossification, the duration of deafness before cochlear implantation, and the preoperative promontory test dynamic range (degree of response on the promontory test in decibels); cause of deafness and residual hearing were not correlated with speech discrimination. Cerebral dominance was indirectly determined by handedness. Handedness laterality was determined by a questionnaire. There was no significant difference in results between patients implanted on their dominant side and patients implanted on their nondominant side. When ears are different according to their peripheral factors, the authors suggest implanting the better ear, provided there is no significant hearing in that ear. When both ears are identical, the side of implantation should be the side of handedness laterality to facilitate device manipulation (a practical reason).