Delusions, misidentifications and hallucinations occur frequently throughout the course of senile dementia of the Alzheimer type (SDAT). Rates of psychosis among subjects with moderate to severe SDAT range from 42% to 84% in our study group; at least half of persons with SDAT with no prior psychiatric history will display psychosis at some point during the course of dementia. Furthermore, psychotic symptoms are associated with accelerated cognitive deterioration, but not with increased mortality.