OBJECTIVE: To investigate the relationship between quadriceps strength and the peak knee adduction moment during walking in medial tibiofemoral osteoarthritis (OA), and whether varus malalignment influences this relationship. METHODS: Maximum isometric quadriceps strength at 60 degrees flexion relative to body mass and the peak knee adduction moment during walking were assessed in 184 community volunteers with medial knee OA. Mechanical knee alignment was determined either directly from full-leg radiograph or extrapolated from anatomic alignment on knee radiograph using regression equations. Pearson's correlation coefficient was used to assess the association between quadriceps strength and peak knee adduction moment. The independent relationship between quadriceps strength and peak knee adduction moment, and the impact of varus malalignment on this relationship, was assessed using multiple regression analyses with and without adjustment for covariates. RESULTS: Quadriceps strength was not significantly associated with peak knee adduction moment (r = 0.14, P = 0.059). Neither quadriceps strength (b = 0.25, P = 0.142) nor the interaction between quadriceps strength and varus malalignment (b = -0.01, P = 0.693) significantly contributed to the variance in peak knee adduction moment. Results were unchanged with the inclusion of covariates. CONCLUSION: No significant association was observed between quadriceps strength and the peak knee adduction moment, and the severity of varus malalignment did not influence the relationship. Results suggest that clinicians should not be concerned that patients with knee OA and stronger quadriceps are more likely to demonstrate a higher knee adduction moment.