Foot orthotics have been used successfully in the treatment of musculoskeletal symptoms associated with structural variations of the foot. Their effectiveness has been primarily addressed through two-dimensional, frontal plane motion studies of the subtalar joint in individuals considered "clinical pronators." Recent evidence suggests that assessment of tibial axial rotation in combination with frontal plane analysis of calcaneal inversion/eversion may provide improved understanding of subtalar joint function. The purpose of this study was to examine the effects of semi-rigid foot orthotics on three-dimensional lower limb kinematics in 20 recreational runners presenting with distinct structural foot characteristics. Radiographic measurements were used to classify subjects into a low or high rearfoot profile group. The results of the kinematic analysis showed a significant orthotic effect for rotations occurring from heel contact to peak tibial internal rotation, as well as in the coupling relationship between tibial axial rotation and calcaneal inversion/eversion. Both groups responded similarly with a mean reduction of 2 degrees in tibial internal rotation. No differences were found for the frontal plane rotations for either group when orthotics were worn. The findings suggest that the maximum effect of orthotics may be realized in the first 50% of stance and related to the changes in tibial axial rotation.