BACKGROUND The purpose of this study was to assess function, at the age of 10 years, of children initially treated nonoperatively for clubfoot with either the Ponseti or French physiotherapy program and to compare outcomes in feet that had undergone only nonoperative treatment with those that required subsequent surgery. METHODS Gait analysis, isokinetic ankle strength, parent-reported outcomes, and daily step activity data were collected when patients who had been treated for idiopathic clubfoot reached the age of 10 years. Patients who had undergone only nonoperative treatment were compared with those who subsequently underwent extra-articular surgery or intra-articular surgery (posterior release or posteromedial release). The clubfoot groups were compared with age-matched controls. RESULTS Of 263 treated clubfeet in 175 patients, 148 had only been treated nonoperatively, 29 underwent extra-articular surgery, and 86 underwent intra-articular surgery (posterior release in 42 and posteromedial release in 44). Significant abnormalities were found in ankle kinetics and isokinetic ankle strength in the feet treated with intra-articular surgery compared with the nonoperatively treated feet (p < 0.017). Compared with controls (n = 40 feet), all groups showed reduced ankle plantar flexion during gait, resulting in a deficit of 9% to 14% for dynamic range of motion, 13% to 20% for ankle moment, and 13% to 23% for power (p < 0.013). Within the intra-articular group, feet that underwent posteromedial release had decreased plantar flexion strength (15%; p = 0.008), dorsiflexion strength (6%; p = 0.048), and parent-reported global function scores (p = 0.032) compared with the posterior release group. The patients with clubfoot took 10% fewer steps (p = 0.015) and had 11% less total ambulatory time (p = 0.001) than the controls. CONCLUSIONS Examination of patients when they had reached the age of 10 years showed better ankle power and isokinetic strength for clubfeet treated without surgery compared with those that underwent intra-articular surgery for residual deformity or recurrence. Compared with controls, both nonoperatively and surgically treated clubfeet had significant limitations in ankle plantar flexion resulting in decreased range of motion, moment, and power. Gastrocnemius-soleus complex strength was decreased after both nonoperative and surgical treatment of clubfeet. Although activity was diminished in the clubfoot population, no differences in function were perceived by the patients' parents. METHODS Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.