© 2018, © The Author(s) 2018. Background: High tibial osteotomy (HTO) is a valuable treatment option in the high-demand patient with chondral damage and an altered mechanical axis. Traditional opening wedge HTO performed with metal plates has several limitations, including hardware irritation, obscuration of detail on magnetic resonance imaging, and complexity of revision surgery. Recently, an all-polyetheretherketone (PEEK) HTO implant was introduced, but no studies to date have evaluated the performance of this implant with minimum 2-year outcomes compared with a traditional metal plate. Purpose: To compare patient outcomes and complications of HTO performed using a traditional metal plate with those performed using an all-PEEK implant. Study Design: Cohort study; Level of evidence, 3. Methods: All patients who underwent HTO by a single surgeon with a minimum 2-year follow-up over a 4-year period were identified. Medical records were reviewed for patient demographics, concomitant procedures, implant used, type and degree of correction, complications, reoperations, and failures. Recorded patient outcomes included EuroQol–5 dimensions (EQ-5D), resiliency, Single Assessment Numeric Evaluation (SANE), Tegner activity level scale, International Knee Documentation Committee (IKDC), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. HTO performed using a traditional metal plate served as the control group. Statistical analysis was performed using the Student t test for continuous variables and chi-square analysis for nonparametric data, with P <.05 considered significant. Results: A total of 41 patients (21 in the all-PEEK group, 20 in the control group) were identified with greater than 2-year follow-up. The mean patient age was 44 years, and there were no differences between the groups with regard to demographics, degree of correction, or concomitant procedures. In addition, no significant differences were found for any of the patient-reported outcomes. Complications (10% vs 15%, respectively; P =.59), failures (10% vs 5%, respectively; P =.58), and reoperations (10% vs 30%, respectively; P =.10) were similar for the all-PEEK and control groups. However, the all-PEEK group did not have any hardware removal, while 4 patients in the control group underwent hardware removal (P =.03). Conclusion: This study suggests that an all-PEEK implant may be safely used with comparable outcomes and complication rates to the traditional method but with less need for hardware removal.