Limited information is available regarding the incidence, nature, and treatment of behavioral problems in Alzheimer's disease (AD). A chart review of 57 outpatients with a diagnosis of AD was conducted to examine these issues. Thirty-three (58%) patients had significant behavioral symptomatology (most commonly delusions, nonspecific agitation, and diurnal rhythm disturbances). Twenty-seven were treated with thioridazine (10-250 mg/day), 15 (55.6%) of whom were judged to have a positive response (mean maximum dose = 55 mg/day). Information regarding the characteristic phenomenology of the behavioral symptoms studied was used to design a clinical rating instrument for AD patients, the Behavioral Pathology in Alzheimer's Disease Rating Scale (BEHAVE-AD), which should be useful in prospective studies of behavioral symptoms as well as in pharmacologic trials.