Rotatory malalignment of the lower extremity in childhood is a very common clinical problem. This malalignment is most frequently due to tibial torsion. Despite the frequency of tibial torsional malalignment, proposed methods of assessment have not found clinical application and the natural history of the deformity is incompletely understood. In this report, a simple clinical method of assessing tibial torsion by calculating the transmalleolar axis is presented. The reproducibility of the method is assessed and the transmalleolar axis is computed in 180 normal children and adults.