In children valgus deformities of the ankle joint are usually due to neurological conditions (spina bifida, poliomyelitis, spasticity). The deformity is characterized by a shortened fibula, wedging of distal tibial epiphysis and valgus tilt of the talus. Other conditions producing similar deformity include congenital and acquired fibular pseudarthroses, multiple exostoses and some cases of tarsal synostosis. Early treatment of a progressive valgus in multiple exostoses is mandatory. The author describes a case of ankle valgus following an undiagnosed traumatic section of tibialis posterior tendon. After predictable failure of a Grice procedure, a persisting good correction was obtained by fibula lengthening combined with talus reposition and fixation on os calcis.