The behavioral and neuropsychiatric symptoms of dementia and Alzheimer's disease have become an increasingly important focus of clinical research. These symptoms also pose a tremendous challenge to families and caregivers. The late afternoon/evening exacerbation of behavioral symptoms in dementia has been recognized by clinicians for >60 years. Researchers have utilized a variety of increasingly sophisticated tools to examine the circadian, hormonal, physiological, and epidemiological correlations with sundowning behavior. Although treatment remains largely empirical, an improved understanding of the complex relationships that drive sundowning behavior should lead to more effective therapies in the future.