Limb lengthening is used to correct leg length discrepancy and to increase stature. The reported frequency of peripheral nerve complications varies from 5% to 30%, but is probably underestimated. Damage may be direct or be caused by overstretching of the nerves. We have used electrophysiological tests to evaluate five patients during bilateral tibial lengthening by the Ilizarov method. Results after 24 to 107 days of lengthening showed electromyographic evidence of partial muscle denervation in all 10 limbs, with reduced motor conduction velocities in two tibial nerves and three common peroneal nerves. The sensory conduction velocity in the sural nerve was always unchanged. A clear relationship was shown between the amount of tibial lengthening and the degree of electrophysiological abnormality. Our results suggest that subclinical nerve damage is a very frequent complication of tibial lengthening.