Background: Currently lateral column lengthening procedure is the one of choice to restore the medial arch and to correct forefoot abduction. This procedure requires a bone graft to expand the osteotomy site either autograft or allograft Objectives: This study aims to evaluate the results of use of a segment of the fibular diaphysis as an autograft to expand the osteotomy site Patients and methods: 28 feet (22 patients) of idiopathic flexible flat foot in children with a mean age of 9.2 years old (average 7.4 – 13.5 years old) were operated by clacanean lengthening osteotomy using a segment of the ipsilateral fibular diaphysis as an autograft. The mean follow up period was 11.2 months (average 9 – 13 months). Results: Patients were evaluated according to clinical and radiological parameters. Clinically 20 cases were classified as very good, seven cases as good while one case was classified as poor. Radiologically one case had failure of graft incorporation with breaking of the graft. Conclusion: The fibular autograft is effective and simple method without significant donor site morbidity when used to expand the osteotomy site in cases of calcanean lengthening osteotomy to correct cases of flexible flat feet