The aim of this study was to establish a protocol for diagnosis and treatment of flexible hindfoot subtalar valgus secondary to spastic cerebral palsy (CP), and to evaluate the results of lengthening of the lateral column of the spastic foot in correction of the foot deformity, pain relief, preservation of subtalar joint mobility, tolerability to orthoses, and overall patient / parent satisfaction. Eighteen ambulatory children (27 feet) with paralytic flexible hindfoot subtalar valgus secondary to spastic cerebral palsy between 4 – 12 years of age were analyzed clinically and radiographically. All of the cases were treated by lateral column lengthening through the calcaneus using the open-wedge osteotomy with insertion of iliac tricortical trapezoid autograft fixed in position by K-wires. Preoperative measurements of certain foot angles were compared with their postoperative values. A new scheme for evaluation of the results using a point scoring system was suggested to evaluate accurately both clinical and radiographic results after a follow-up period of an average of 1.6 years. A new radiographic talocalcaneal length ratio was identified and found to be constant (0.7 – 0.78). Five feet (18.5%) had excellent, 17 (63%) had good, and 5 (18.5%) had fair outcomes. There was neither poor outcome (0%), nor significant complications. Lateral column lengthening can be considered superior to foot surgeries that arthrodise the subtalar joint as it combines both correction of the foot deformity and preservation of the subtalar joint mobility.