We studied two unrelated patients with cerebrotendinous xanthomatosis, in whom clinical examination revealed central nervous system long tract involvement. Brain and spinal cord magnetic resonance imaging showed no signs supporting the involvement of the long pathways. Somatosensory and motor evoked potentials demonstrated central sensory and motor conduction abnormalities, which suggested distal degeneration of longer fibers, rather than scattered focal lesions in the CNS. In one of the patients the neurophysiological study was repeated 6 and 12 months after the beginning of treatment with chenodeoxycholic acid, showing a progressive improvement. Therefore, our data suggest that central motor and sensory conduction studies may be useful in the assessment of the disease and in monitoring treatment.