The Neuropsychiatric Inventory (NPI) was developed to assess psychopathology in dementia patients. It evaluates 12 neuropsychiatric disturbances common in dementia: delusions, hallucinations, agitation, dysphoria, anxiety, apathy, irritability, euphoria, disinhibition, aberrant motor behavior, night-time behavior disturbances, and appetite and eating abnormalities. The severity and frequency of each neuropsychiatric symptom are rated on the basis of scripted questions administered to the patient's caregiver. The NPI also assesses the amount of caregiver distress engendered by each of the neuropsychiatric disorders. A total NPI score and a total caregiver distress score are calculated, in addition to the scores for the individual symptom domains. Content validity, concurrent validity, inter-rater reliability, and test-retest reliability of the NPI are established. Different neurologic disorders have characteristic neuropsychiatric manifestations and distinctive NPI profiles. The NPI is sensitive to treatment effects and has demonstrated the amelioration of behavioral symptoms in Alzheimer's disease by cholinergic agents. The NPI is a useful instrument for characterizing the psychopathology of dementia syndromes, investigating the neurobiology of brain disorders with neuropsychiatric manifestations, distinguishing among different dementia syndromes, and assessing the efficacy of treatment.