Aims. After the initial correction of congenital talipes equinovarus (CTEV) using the Ponseti method, a subsequent dynamic deformity is often managed by transfer of the tendon of tibialis anterior (TATT) to the lateral cuneiform. Many surgeons believe the lateral cuneiform should be ossified before surgery is undertaken. This study quantifies the ossification process of the lateral cuneiform in children with CTEV between one and three years of age. . Patients and Methods. The length, width and height of the lateral cuneiform were measured in 43 consecutive patients with unilateral CTEV who had been treated using the Ponseti method. Measurements were taken by two independent observers on standardised anteroposterior and lateral radiographs of both feet taken at one, two and three years of age. Results. All dimensions of the lateral cuneiform on the affected side increased annually but remained smaller than the corresponding dimensions of the unaffected foot (p < 0.01). The lateral cuneiform resembled a 9 mm cube at two years and an 11 mm cube at three years. Conclusion. At one and two years, the ossification centre of the lateral cuneiform may not be large enough to accommodate a drill hole for tendon transfer. However, by three years, it has undergone sufficient ossification to do so. Cite this article: Bone Joint J 2017;99-B:1109–14