Congenital dificiency of the fibula has a clinical spectrum ranging from partial deficiency to complete absence. The major clinical problems are the severe leg-length discrepancy and the deformities of the foot and ankle. The traditional method of compensation for severe leg-length discrepancy has been ablation of the forepart of the foot by the Symeor Boyd method and subsequent fitting of a prosthesis. The development of newer techniques of limb-lengthening with Ilizarov apparatus in recent years has changed the concept of treatment. The authors have treated 5 patients with congenital deficiency of the fibula by the Ilizarov lengthening method at the Department of orthopedic Surgery, Seoul National University Hospital between Feb, 1989 and Dec. 1992. Five patients had leg length shortening rainging from 6.0cm to 9.3cm(average, 7.6cm) and had surgery at an average age of 9.1 years. The leg length discrepancy was projected to average 10.7cm(range, 8.8cm-13.3cm). Leg length equalization was achieved by one stage lengthening in 4 of 5 patients with an average 8.3cm(range, 6.0cm-12.4cm) lenthening. In one patient, there was 3.5cm residual shortening even after 8.1cm of lengthening. Complications were encountered in 4 patients: recurrent foot deformities in 3 cases, temporary knee flexion contracture in 3 cases, and stress fracture at the regenerated site in 1 case. In all 3 Acterman and Kalamchi's Type II cases, the width of distal tibial physis apparantly narrowed down after lengthening of average 9.3cm(average 51.8% lengthening, 33.4-73%). We found that in congenital deficiency of the fibula the Ilizarov method was effective to achieve lengthening and to correct deformities, unless there were severe shortening of the leg and complex three-plane deformity of the foot and ankle. However, excessive lengthening in one stage should be avoided to prevent recurrence of valgus deformity and growth plate damage of the tibia.