Neuropsychiatric symptoms such as delusions and misidentifications have been reported in dementia ranging from 10% to 73% in Alzheimer's disease (AD) patients and up to 40% in multi-infarct dementia (MID) patients. The aim of this study was to investigate in 61 AD and 31 MID patients both the frequency and the content of delusions during the course of illness and to evaluate the relationship between these and both functional and mental decline. The results indicated that delusion experiences had occurred in 45% of AD patients and in 38% of MID patients, occurring most frequently during the first year of illness. Patients who experienced psychiatric symptoms showed higher mini mental state examination scores and were less impaired in functional disability measures. With regard to the content, no significant differences were observed between AD and MID patients; 53% of psychotic symptoms were found to be paranoid delusions while 47% were misidentification delusions.