Predetermination of leg length discrepancy, which has to be expected in patients with congenital defects of the fibula, is very useful for the treatment program. Taking morphologic aspects and the principles of growth into consideration it is possible to predict quite accurately the final leg length in unilateral fibula defect. The prognosis is based on the finding, that the percentage longitudinal deficiency is constant during the growth of the lower limb. The calculation of the absolute leg length is done by assistance of the diagrams by Anderson and coworkers. The overall length discrepancy of unilateral hypoplasia of the fibula exceeds 8.5 cm. In cases of fibula aplasia a discrepancy of more than 10 cm. has to be expected. We saw this severe deformity on more than 50% of our cases. Experience supports the conclusion that preservation of the foot even by a number of reconstructive operations gives mostly better results than early amputation and provision of a prosthesis. There is a good chance to achieve limb-length equality by operations in cases of fibula hypoplasia type IA and IB. This chance is limited in hypoplasia type II and absence of the fibula.