Background: Preserving residual low-frequency hearing is an important goal in modern cochlear implantation, particularly for electro-acoustic stimulation candidates. Electrode design may influence cochlear trauma and hearing outcomes, but direct comparisons between slim perimodiolar (PM) and lateral wall (LW) arrays remain limited. Aims: To compare hearing preservation outcomes between new-generation PM and LW electrodes in adult cochlear implant recipients and identify predictors of successful preservation. Methods: A retrospective cohort study was conducted at the NextSense Cochlear Implant Centre, Sydney, including 333 adults implanted between 2015 and 2021. All had normal cochlear anatomy and preoperative low-frequency four-frequency pure-tone averages (FFPTA) ≤80 dB HL. Patients received either LW (CI522/622, n=244) or PM (CI532/632, n=89) electrodes. Hearing preservation was defined as a postoperative threshold shift ≤20 dB at FFPTA or 250 Hz, or any measurable residual hearing. Regression and ROC analyses assessed predictors of preservation. Results: Hearing preservation rates were comparable between groups (36.3% LW vs 36.4% PM, p=0.992). Mean threshold shifts at 250 Hz were similar (LW: 33.2 dB; PM: 31.2 dB, p<0.0001). Increasing age predicted poorer preservation in the PM group (p=0.0079) but not in the LW group. Lower preoperative FFPTA correlated with greater likelihood of preservation in both. Conclusion: Both slim PM and LW arrays achieved favourable and equivalent hearing preservation outcomes. Age and preoperative thresholds were significant predictors, supporting the importance of tailored electrode selection and atraumatic surgical technique for optimal preservation.