A structural graft is often used to maintain correction and achieve union after anterior calcaneal lengthening osteotomy for treatment of flexible flatfoot. Autograft, the current gold standard, is limited in availability and configuration and is associated with donor site morbidity in as much as 48%, whereas the alternative allograft carries risks of disease transmission and collapse. Polyaryletherketone cage, with a healing rate similar to that of autograft, high stability, and no donor-site morbidity, has been used in spine surgery. However, its use has not been documented in foot and ankle surgery. We reviewed 15 patients with painful flatfeet after failure of conservative treatment who were treated by anterior calcaneal lengthening osteotomy using polyaryletherketone cage instead of bone graft. Minimum follow-up was 1 year (average, 1.27 years; range, 1-1.5 years). The male-female ratio was 1:1.5 (six males, nine females). Mean age at time of surgery was 10.8 ± 1.7 years (range, 8-13.5 years). Minimum follow-up was 1 year (average, 1.27 years; range, 1-1.5 years). Nine patients had a unilateral procedure and three had a simultaneous bilateral procedure, for a total of 15 operated feet (seven right and eight left). The paired t-test result was statistically significant in comparison of radiographic measurements at presurgery and postsurgery with P value <0.001. All cases showed full union clinically and radiographically at last follow-ups and no complications occurred. Our data suggest that polyaryletherketone cage may be used as a structural graft option for anterior calcaneal lengthening osteotomy.