Background: Unicompartmental knee replacement (UKR) can provide reliable clinical and functional outcomes when performed simultaneously in both knees for treating bilateral osteoarthritis (OA). No studies to date have evaluated gait pattern after simultaneous bilateral UKR. The aim of this study was to evaluate changes in gait variables after bilateral single-stage UKR (B-UKR) and to compare them with the outcomes after unilateral UKR in two other groups of patients: one with bilateral knee OA (P-UKR) and one with the contralateral knee unaffected (H-UKR). Methods: Three-dimensional motion cohort data were prospectively collected before and six months after surgery; 37 were allocated to the B-UKR (n =13), P-UKR (n= 12) or H-UKR (n = 12) group. Spatiotemporal variables (stride length, gait speed, gait cadence, stance phase, swing phase, and double support phase) and kinematic parameters (knee flexion and extension peak values, knee range of motion (ROM), and hip abduction peak value) were analyzed using mixed analysis of variance (ANOVA). The magnitude of effect for significant outcomes (ES) was determined using Cohen's d. Results: Postoperative improvement in gait cadence (P b 0.01; ES=1.20), walking speed (P b 0.05; ES = 0.58), stride length (P b 0.05; ES = 0.67), knee ROM (P b 0.05; ES = 0.89), knee flexion (P b 0.05; ES=0.94), and hip abduction (P b 0.001; ES=1.16) was noted for the BUKR group, whereas only stride length improved (P b 0.05; ES=0.48) for the H-UKR group, and no changes in any gait parameter were seen for the P-UKR group. Conclusions: Postoperative improvement in gait parameters was observed in the B-UKR patients with bilateral OA. Whenever possible, simultaneous bilateral UKR should be considered in such patients.