High knee joint-loading increases the risk and progression of knee osteoarthritis (OA). Mechanical loading on the knee is reflected in the external knee adduction moment (KAdM) that can be measured during gait with laboratory-based measurement systems. However, clinical application of these systems is limited. Ambulatory movement analysis systems, including instrumented force shoes (IFS) and an inertial and magnetic measurement system (IMMS), could potentially be used to determine the KAdM in a laboratory-free setting. Promising results have been reported concerning the use of the IFS in KAdM measurements; however its application in combination with IMMS has not been studied. The objective of this study was to compare the KAdM measured with an ambulatory movement analysis system with a laboratory-based system in patients with knee OA. Gait analyses of 14 knee OA patients were performed in a gait laboratory. The KAdM was concurrently determined with two the systems: (i) Ambulatory: IFS and IMMS in combination with a linked-segment model (to obtain joint positions); (ii) Laboratory: force plate and optoelectronic marker system. Mean differences in KAdM between the ambulatory and laboratory system were not significant (maximal difference 0.20. %BW*H in late stance, i.e. 5.6% of KAdM range, P>0.05) and below clinical relevant and hypothesized differences, showing no systematic differences at group level. Absolute differences were on average 24% of KAdM range, i.e. 0.83. %BW*H, particularly in early and late stance. To achieve greater accuracy for clinical use, estimation of joint position via a more advanced calibrated linked-segment model should be investigated. © 2012 Elsevier Ltd.