The purpose of the present study was to compare bilateral external knee moments during gait in patients with concomitant medial compartment knee OA, varus alignment and chronic anterior cruciate ligament (ACL) deficiency who underwent either medial opening-wedge high tibial osteotomy alone (HTO) or simultaneous HTO and ACL reconstruction (HTO-ACLR). Fifty-two patients (26 matched pairs) completed 3D gait analysis preoperatively and at a minimum 5 years postoperatively. Patients were matched for preoperative age, sex, body mass index and magnitude of correction. Primary outcomes selected a priori were the peak knee adduction moment (KAM) and knee flexion (KFM) moment during stance. Moments were compared using mixed model repeated measures analysis of variance (ANOVA). For the peak KAM, there was a significant time by limb interaction. For both groups, there were similar reductions in the peak KAM 5 years postoperatively in the surgical limb only [-1.34 %BW × Ht (-1.71, -0.96) and -1.72 %BW × Ht (-1.99, -1.44) for HTO and HTO-ACLR, respectively]. For the peak KFM, there was a significant time by group by limb interaction. There was a decrease in the peak KFM 5 years postoperatively in the HTO group [-0.88 %BW × Ht (-1.45, -0.31)] but not in the HTO-ACLR group [0.03 %BW × Ht (-0.43, 0.48)]. These results suggest that individuals with medial knee OA, varus alignment and chronic ACL deficiency who undergo simultaneous medial opening-wedge HTO and ACL reconstruction may not experience the same long-term (5 year) changes in sagittal plane knee biomechanics observed in patients undergoing HTO alone. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.