The Foot Posture Index is a new multidimensional and multiplanar tool aimed at quantifying the degree of pronation to supination of the foot, comprising eight criteria that sum to produce a final "score" of foot posture. In an initial study involving 31 subjects, angulations measured from dorsoplantar and lateral radiographs were compared with the corresponding Foot Posture Index criteria using Spearman's rho and the generalized linear model of analysis of variance. Eleven of the participants from Study 1 completed a second study in which wedges were used to alter foot position to determine whether changes to foot position were sensitively reflected in Foot Posture Index criterion scores and associated radiographic images. Study 1 demonstrated a significant correlation for only one criterion (talar head palpation), while Study 2 demonstrated intrasubject sensitivity to overall changes from supinated to pronated and supinated to resting positions but insensitivity to changes from resting to pronated positions. The results suggest that although the Foot Posture Index could be a useful tool to broadly classify foot postures, it is not sensitive to all small movements when assessed by this method.