BACKGROUND: Decreased motion of the subtalar joint is common after operative treatment of idiopathic clubfeet. The purposes of this study were to validate parameters of dynamic foot-pressure measurement that enable detection of physiological pronation of the subtalar joint and to analyze the consequences of absent or decreased pronation following clubfoot surgery on long-term functional results. METHODS: To validate parameters of dynamic foot-pressure measurement, we initially analyzed two control groups: one of forty asymptomatic normal feet and the other of five feet with a previous subtalar joint arthrodesis. The resulting parameters were then applied to a group of nineteen patients with twenty-four idiopathic clubfeet for whom initial conservative treatment had failed and in whom a posterior surgical release (lengthening of the Achilles tendon and release of the posterior ankle capsule) had been performed at a mean age of twenty months. The mean duration of follow-up was forty-one years. All feet were evaluated radiographically, and the clinical results were assessed with the American Orthopaedic Foot and Ankle Society score. RESULTS: An interruption in the rise of the pressure-time curve and a short medial deviation of the center of pressure path immediately after heel strike are reliable and objective characteristics of pronation movement of the subtalar joint. Nineteen clubfeet had a demonstrable pronation movement, and five clubfeet did not. The nineteen feet with pronation movement were either asymptomatic (twelve feet) or mildly painful on occasion (seven feet). The mean American Orthopaedic Foot and Ankle Society score for the nineteen feet was 87 points. The five feet without pronation movement were moderately painful during strenuous activities only (four feet) or were nearly always painful (one foot). The mean score for those feet was 57 points. There was a significant difference between these two groups with regard to the pain scores and the total scores (p < 0.001), but there was no appreciable difference regarding function and hindfoot motion. It was not possible to distinguish between these two groups on the basis of the findings of the physical or radiographic examinations. CONCLUSIONS: Idiopathic clubfeet with preserved hindfoot pronation have a better long-term prognosis. Preservation of functional mobility of the subtalar joint is a key factor in the treatment of clubfoot deformity.