• Seven months following severe crushing closed-head trauma with initial excellent recovery, neurologic deficits referable to the right mesencephalon abruptly developed in a 28-year-old man. Computed tomography demonstrated a cystic midbrain lesion with apparent communication with the aqueduct (later confirmed at autopsy). Brain-stem auditory evoked potentials after the clinical deterioration showed depression of amplitude of wave V, compared with predeficit records, only when the ear contralateral to the brain-stem lesion was stimulated.