To date, corticospinal tract functional integrity in ataxia-telangiectasia has not been studied. Thorough evaluation of central motor pathways is also lacking in neuropathologic and clinical studies. Using electromagnetic stimulation, we assessed the integrity of the corticospinal tracts in eight patients with ataxia-telangiectasia. Cortical and peripheral compound motor action potentials were recorded from the abductor pollicis brevis muscle. Recordings of the shortest F-wave latency and of the compound motor action potential distal latency were made from the abductor pollicis brevis muscle after electrical stimulation of the median nerve at the wrist. A significant increase in central motor conduction time was observed in four patients, two of whom had clinical findings compatible with a pyramidal lesion. This study demonstrates involvement of the central motor pathways in ataxia-telangiectasia, which appears to be more frequent late in the course of the disease.