Regardless of the mode of treatment, clubfoot has a strong tendency to relapse, especially hindfoot equinus. Because contraction or shortening of the Achilles tendon causes an equinus deformity of the ankle, release of this tendon is required to correct equinus deformity in patients with residual or relapsed clubfoot. This study assessed the effectiveness of the Vulpius technique in correcting equinus deformity in patients with residual or relapsed clubfoot. Of the 80 idiopathic clubfeet treated conservatively using the Ponseti protocol, between March 2000 and July 2008, 32 were found to have residual or relapsed equinus deformity, with 22 feet in 17 patients undergoing Vulpius-type Achilles tendon lengthening. Mean age at the time of surgery was 29 (range, 6 to 52) months, and mean follow-up was 48 (range, 24 to 78) months. Clinical evaluation included the dorsiflexion angle of the ankle and radiographic evaluation included the talocalcaneal and tibiocalcaneal angles on dorsiflexion lateral views. All 22 feet showed satisfactory results at last follow-up, with significant improvements in mean ankle dorsiflexion angle, mean tibiocalcaneal angle, and mean lateral talocalcaneal angle (p < .05 each). The Vulpius procedure is an effective surgical procedure for correcting equinus deformity in residual and relapsed clubfeet.