Event-related potentials (ERPs) are important clinical and research instruments in neuropsychiatry, particularly due to their strategic role for the investigation of brain function. These techniques are often underutilized in the evaluation of neurological and psychiatric disorders, but ERPs are noninvasive instruments that directly reflect cortical neuronal activity. Previous studies using the P300, P3a, and MMN components of the ERP to study dementing illness are reviewed. The results suggest that particularly the P300 brain potential is sensitive to Alzheimer's disease processes during its early stages, and that easily performed stimulus discrimination tasks are the clinically most useful. Finally, these data suggest that the P300 ERP can aid in the diagnosis of dementia and may help in the assessment of early Alzheimer's disease.