This study investigated the clinical usefulness of the contingent negative variation (CNV) as a neurophysiological index of cognitive dysfunction associated with cerebrovascular disease. A total of 31 patients ranging in age from 45 to 88 years with the diagnosis of a stroke were included. Nineteen patients were classified as demented according to clinical assessment and the Mental Deterioration Index (MDI) based on the WAIS, the other 12 patients as non-demented. In a discriminative CNV-paradigm two different tones served as warning stimuli for a flash of light presented 1.5 s later that could be turned off by a press on a button only after the relevant tone. According to our hypothesis, CNV amplitudes of demented patients were significantly smaller than those of the non-demented group. Moreover, a significant relationship was observed between severity of dementia (MDI) and degree of amplitude reduction. Thus, it was concluded that the CNV method could make an important clinical contribution to the assessment and course of dementia.