Summary:Advanced age and dementia are well-known risk factors for delirium, and most studies of delirium have concentrated on hospitalized populations. We reviewed the records of 199 community-dwelling Alzheimer disease (AD) patients and identified 43 (22%) who had had episodes of delirium during their dementing illness. These patients were matched for age, gender, and disease duration to AD patients without previous episodes of delirium. Variables examined included causes of delirium, Mini-Mental State Examination scores, Clinical Dementia Rating scores, Blessed Activities of Daily Living (ADL) scores, years of education, neuropsychological performance, and incidence of behavioral symptoms on the Brief Psychiatric Rating Scale. In six of 198 (3%) patients delirium was an initial symptom of AD. Conditions associated with onset of delirium were urinary tract infections, stressful events, surgery, medical illnesses, and medications. No significant differences were found between groups on neuropsychological testing. Patients with previous episodes of delirium had worse ADL scores and higher disease-course incidences of hallucinations and paranoid delusions, mostly occurring during the delirious episode. We conclude that delirium is common in AD, but it is an unusual initial symptom and it occurs in diverse clinical settings. Measures of behavioral symptoms and ADLs are more likely to reflect the impact of delirium on clinical status than measures of cognition or stage of dementia.