Objective: We investigated the frequency and inter-relationship of neuropsychiatric disturbances in a population sample of persons suffering from Alzheimer's disease (AD). Method: Screening 5,092 elderly residents (90% of the population aged 65 and older) of Cache County, Utah, for dementia, we identified 198 persons with AD using a comprehensive neuropsychiatric examination protocol. This examination included the Neuropsychiatric Inventory (NPI), a widely used measure of dementia-associated neuropsychiatric disturbances. Results: Overall, 60% of individuals with AD reported one or more neuropsychiatric symptoms. A latent class analysis revealed that these participants could be classified into three groups (classes) based on their neuropsychiatric symptom profile. The largest class included cases with no neuropsychiatric symptoms (40%) or with a mono-symptomatic disturbance (19%). A second class (28%) exhibited a predominantly affective syndrome, while a third class (13%) had a psychotic syndrome. Conclusion: Data from this first US population-based study of AD-associated neuropsychiatric disturbances suggest that a significant majority of persons with AD suffer from one or more neuropsychiatric disturbance. Based on phenomenological study, the spectrum of neuropsychiatric symptoms in AD can be empirically classified into three groups: an affective syndrome, a psychotic syndrome and other neuropsychiatric disturbance. The biologic and predictive validity of this classification merits further investigation.