OBJECTIVE: The goal of this investigation was to study the prevalence of delusions in Alzheimer's disease and to compare the performance of the delusional and nondelusional groups on a neuropsychological test battery. METHOD: The authors studied 107 patients with Alzheimer's disease and 51 age- and education-comparable normal subjects using a standardized psychiatric interview and a neuropsychological test battery. RESULTS: Thirty-seven patients with Alzheimer's disease had delusions with or without hallucinations. Patients with delusions were significantly more impaired than those without delusions (and the normal comparison group) on the Mini-Mental State examination; Blessed Information-Memory-Concentration Test; Dementia Rating Scale, especially its conceptualization and memory subtests; and a test of verbal fluency. The delusional group also tended to be somewhat more impaired than the nondelusional group on the modified Wisconsin Card Sorting Test and the similarities subtest of the Wechsler Adult Intelligence Scale-revised. CONCLUSIONS: Approximately one-third of patients with Alzheimer's disease had developed psychotic symptoms sometime after the onset of dementia. The presence of psychotic symptoms in Alzheimer's disease was associated with greater cognitive impairment, especially frontal/temporal dysfunction, and possibly with a more rapidly progressive dementia.Abstract Teaser