Although Alzheimer's original description of the dementing disorder that bears his name emphasized the prominence of troublesome and disruptive behaviors, a systematic investigation of behavioral disturbances of dementia did not begin in earnest until the 1980s. At that time, as the neuropathologic identity of presenile Alzheimer's disease and late-onset “senile dementia” was recognized, the redefinition of Alzheimer's disease abruptly increased the number of patients diagnosed with this condition. Physicians and other medical personnel working with Alzheimer's disease patients recognized both the importance of abnormal behaviors in this now large patient population and the need to describe, classify, and quantify these behaviors.