To compare functional hearing preservation (HP) with a slim perimodiolar array (SPA) and a slim lateral wall array (SLW) in cochlear implantation (CI). Retrospective chart review. Tertiary referral center. All adult, post-lingual CI recipients with serviceable preoperative hearing serially implanted with SPA or SLW electrodes from July 2015 through July 2018. Cochlear implantation. Hearing preservation (HP). Patients with a low frequency pure-tone average (LFPTA) (125, 250, 500 Hz) threshold less than 80 dB were considered HP candidates based on preoperative audiograms. Postoperative audiograms were obtained before activation. Successful HP was defined as retention of LFPTA less than 80 dB. The change in LFPTA (ΔLFPTA) was also calculated. One hundred twenty one patients were implanted with either the SPA or SLW electrodes, 82 (42,40) of whom were HP candidates with postoperative audiograms. Average (standard deviation, SD) preoperative LFPTA was 54.86 [19.38] and 54.38 [13.58] dB for SLW and SPA respectively, with a mean ΔLFPTA of 24.6 [15.94] and 24.92 [16.66] dB. Successful HP was achieved in 21 (50%) and 22 (55%). Preoperative LFTPA, ΔLFPTA, and postoperative LFPTA were not significantly different (p = 0.89, 0.75, 0.93) between electrodes. The SPA is as effective at immediate functional HP after CI as a SLW.