OBJECTIVES/HYPOTHESIS An increasing number of patients with low-frequency residual hearing are fitted with a cochlear implant. The challenge is to optimize cochlear implant device properties and develop atraumatic surgical techniques to preserve residual hearing. In view of the ongoing debate about the optimal procedure for opening the cochlea during cochlear implantation, we reviewed the evidence on the round window and the cochleostomy insertion techniques and compared their effects on postoperative residual hearing. DESIGN Systematic review. METHODS Electronic databases were systematically searched for relevant studies published up to January 2012. All studies reporting on residual hearing and hearing preservation surgery were included. RESULTS Sixteen studies, with a total of 170 patients, were included. There were no studies directly comparing both surgical insertion techniques. The methodologic quality of the studies was poor and might be subjected to a high risk of bias. Because there were no studies directly comparing the 2 techniques and controlling for possible influencing factors, differences between studies might also be influenced by intersurgeon variance in many facets regarding cochlear implantation surgery. The available data show a postoperative low-frequency hearing loss ranging from 10 to 30 dB at 125, 250, and 500 Hz, regardless of surgical technique. The number of patients with a postoperative complete hearing preservation ranged from 0% to 40% for the cochleostomy group and from 13% to 59% in the round window group. CONCLUSION The available data do not show that there is a benefit of one surgical approach over the other regarding the preservation of residual hearing. To provide solid evidence, a double-blind randomized trial is needed, which compares the clinical outcomes, notably the degree of hearing preservation, of both surgical approaches.