We investigated the range of behavioral abnormalities in patients with Alzheimer's disease (AD) compared with normal age-matched control subjects. The range of behavioral disturbances manifested and the relationship between specific abnormalities with the level of cognitive impairment have not been established. Fifty consecutive outpatients with mild (n = 17), moderate (n = 20), and severe (n = 13) AD and 40 age-matched normal controls were evaluated for behavioral abnormalities occurring in the month preceding the interview. The caregivers of the patients and the spouses of the control subjects were interviewed with the Neuropsychiatric Inventory (NPI). The frequency and severity of the following 10 behaviors were assessed: delusions, hallucinations, agitation, dysphoria, anxiety, euphoria, apathy, disinhibition, irritability, and aberrant motor behavior. Correlations among these 10 behaviors and their relationship with cognitive impairment were also investigated. Eighty-eight percent of AD patients had measurable behavioral changes. All 10 behaviors were significantly increased in the AD patients compared with normal subjects. The most common behavior was apathy, which was exhibited by 72% of patients, followed by agitation (60%), anxiety (48%), irritability (42%), dysphoria and aberrant motor behavior (both 38%), disinhibition (36%), delusions (22%), and hallucinations (10%). Agitation, dysphoria, apathy, and aberrant motor behavior were significantly correlated wit cognitive impairment.