To clarify the diagnostic value of neurophysiological investigations in patients with Cockayne's syndrome (CS). The study involved two patients with clinical diagnoses of classical and severe CS, who were neurophysiologically evaluated by means of: (1) multimodal visual (VEPs), brainstem auditory (BAEPs) and upper limb somatosensory (SEPs) evoked potentials; (2) electroretinography; and (3) nerve conduction and needle electromyography studies. Both patients showed multimodal evoked potential (EP) signs of central nervous system involvement that overlapped in severity and extent, and were consistent with demyelination along the central sensory pathways. Flash VEPs and SEPs were more altered than pattern VEPs and BAEPs. No signs of retinopathy or hearing loss of cochlear origin were detected. The nerve conduction and needle electromyography studies showed severe signs of sensory and motor demyelinating and axonal peripheral neuropathy. Peripheral neuropathy was clinically uncertain. There were no significant differences between the two patients. Our results show that combined multimodal EP and nerve conduction studies are diagnostically highly sensitive even in the early stage of CS, but their ability to distinguish classical and severe CS is limited. The unusual features were characterised by the absence of clinical and electrophysiological signs of otherwise common retinopathy and neurosensory hearing loss. BAEPs seem to be more useful than VEPs or SEPs in the diagnostic work-up of patients with suspected CS.