Neuropsychological assessment involves the observation and measurement of an individual's behavior in relation to a given stimulus that has been selected for its likelihood to provoke an abnormal response in the presence of neurological damage. This approach incorporates a medical and psychological approach to diagnosis in that both pathology-specific signs and deviations from normal distributions are examined. In the case of Alzheimer's disease (AD), this methodology has assumed considerable importance. This is because behavioral indicators remain the principal basis for provisional diagnosis when there are no biological markers. Observations of elderly persons with and without senile dementia have led to the development of stimuli, or tests, that are able to assess the functioning of specific cognitive processes affected in AD as opposed to more common age-associated changes. Many of these tests have been found to be culturally portable. Diagnostic difficulties arise principally from the fact that many neuropsychological tests cannot be used in isolation, from uncertainty as to the limits of "normal" functioning and from the psychometric problems related to pathological thresholds and item-weighting. The usefulness of neuropsychological testing in the future could undoubtedly be enhanced by the use of measures derived from indices of decline in functioning rather than normative data and the development of functional testing in collaboration with cerebral imaging.