Developmental coxa vara (DCV) develops during early childhood between the age of independent walking and 6 years. The deformity includes a decrease in the neck–shaft angle and femoral retroversion. Recently, good results have been reported using external fixator systems for the correction of proximal femoral deformities secondary to slipped capital femoral epiphysis, Perthes’ disease in children, and percutaneous proximal femoral osteotomy for coxa vara. This preliminary study was performed to evaluate the results of percutaneous subtrochanteric osteotomy in restoring the normal alignment and orientation (radiographic outcome), thereby restoring the normal mechanics of the hip joint, overcoming shortening of the limb, and re-establishing the length–tension relationship of the abductor muscles (functional outcome). During the period between January 2009 and January 2012, a prospective study was conducted involving 30 (33 hips) patients with DCV and a preoperative Hilgenreiner’s epiphyseal angle of 60° or greater on coronal radiographs. Clinical and radiological (anteroposterior radiograph of the pelvis) evaluation of patients was carried out preoperatively and postoperatively until union was achieved and fixator removal was carried out, and then at 6 months and at the final follow-up, with a minimum of 12 and a maximum of 33 months after surgery and an average of 20.8 months. We used the technique described by Sabharwal and colleagues (2005) to perform an acute, opened wedge subtrochanteric valgus-flexion-derotation femoral osteotomy using a percutaneous multiple drill hole technique. A low-profile Ilizarov external fixator was applied in each case. The average operative time (including anesthesia time) was 74 (range 60–130) min. The average time spent in the external fixator until union was 11 (range 7–15) weeks. The average intraoperative blood loss was 35 (range 10–150) ml, and no patient developed hemodynamic instability or required any postoperative blood transfusion. The hospital stay averaged 1.2 (range 1–2) days. Hilgenreiner’s epiphyseal angle preoperatively averaged 70.6° (ranging from 55° to 90°). At 6 months it averaged 40.6° (ranging from 15° to 60°). At final follow-up it averaged 41.16° (ranging from 15° to 60°). Percutaneous subtrochanteric osteotomy with external fixation appears safe and effective in treating multiplanar proximal femoral deformities associated with DCV in children. Level of Evidence: Level IV.