The purpose of this study was to test the hypothesis that a positional fault occurs at the distal tibiofibular joint when the foot is inverted beyond its normal range (Mulligan 1995). Seventeen normal subjects, two subjects with a chronic tendency to ‘go over’ on one or both ankles and six patients with acutely sprained ankles were positioned in supine lying with the foot to be tested in the subtalar neutral position. An anteroposterior (AP) mobilization was then performed on the lateral malleolus of the right and left ankles of all those included in the study. The movement that occurred at the distal fibula as a result of this mobilization was recorded and plotted against the force required to produce it. The slopes of the graphs from the three groups of subjects were statistically analysed using the appropriate t tests. Results indicated that a significantly greater amount of movement per unit force occurred in one third of the patients with acutely sprained ankles (P = 0.01%, P = 0.09%). These results lend support to the hypothesis that a positional fault occurs at the inferior tibiofibular joint in ankle sprain patients. This could have exciting implications for the future direction of the treatment of these injuries.