Delirium and dementia are common causes of cognitive impairment in older populations. Although each may occur independently, delirium and dementia frequently coexist. Dementia is a leading risk factor for delirium, and there is an increased incidence of new dementia and cognitive decline after delirium. Delirium can accelerate the rate of cognitive decline, suggesting that an episode of delirium can result in a more rapid progression of dementia symptoms, leading to earlier functional disability, increased caregiver burden, and rising health care costs. As the population ages, there has been a rapid increase in the incidence and prevalence of delirium and dementia. Better understanding of the risk factors, outcomes, and mechanistic associations between these 2 conditions is therefore critical for developing successful prevention and treatment strategies for this increasing problem.