Abstract: The effect of facial behaviour on gaze tracking accuracy was studied while using a prototype system that integrated head-mounted, video-based gaze tracking and a capacitive facial movement detection for respective pointing and selecting objects in a simple graphical user interface. Experiments were carried out to determine how voluntary smiling movements that were used to indicate clicks affect the accuracy of gaze tracking due to the combination of user eye movement behaviour and the operation of gaze tracking algorithms. The results showed no observable degradation of the gaze tracking accuracy when using voluntary smiling for object selections.