OBJECTIVE: The purpose of the study was to develop a standardized instrument, the Behavior Rating Scale for Dementia, for rating psychopathology in patients with probable Alzheimer's disease and to conduct a multicenter pilot study of this instrument. METHOD: The rating scale was developed collaboratively on the basis of clinical experience and existing instruments. Items were scaled according to frequency of psychopathology and were administered to an informant who was familiar with the subject. The scale was administered in a standardized manner by trained examiners who had met predetermined certification standards. The study group consisted of 303 subjects with probable Alzheimer's disease who had undergone standardized clinical evaluations by the Consortium to Establish a Registry for Alzheimer's Disease. RESULTS: Subjects had an average of 15 problems rated as present in the preceding month. Wide variability in the nature of disturbances was found, with a number of items rated as present since the illness began but not in the past month. Interrater agreement was high. Factor analysis suggested eight preliminary factors that mapped onto clinically relevant domains: depressive features, psychotic features, defective self-regulation, irritability/agitation, vegetative features, apathy, aggression, and affective lability. CONCLUSIONS: The Behavior Rating Scale for Dementia provides a standardized, reliable measure that can be administered to caregivers of demented subjects. On the basis of the present study, the scale has been revised slightly. After additional studies in progress, the Behavior Rating Scale for Dementia will be available for general use in assessing a wide range of psychopathology in dementia.