Objective The aim of this study is to provide an overview of prevalence, symptoms, risk factors and prognosis of delirium in primary care and institutionalized long-term care. Design The method used in this study is a systematic PubMed search and literature review. Results The prevalence of delirium in the population among the elderly aged 65+?years is 12%. Prevalence rises with age: 10% among a general population aged 85+?years. Prevalence rises up to 22% in populations with higher percentages of demented elder. In long-term care, prevalence ranges between 1.4% and 70%, depending on diagnostic criteria and on the prevalence of dementia. There is a significant increase of the risk of delirium with age and cognitive decline in all groups. Concerning prognosis, most studies agree that older people who previously experienced delirium have a higher risk of dementia and a higher mortality rate. Population and long-term care studies show the same tendency. Conclusions Delirium in a non-selected population aged 65+?years is uncommon. However, prevalence rises very quickly in selected older groups. Primary care doctors should be aware of a relatively high risk of delirium among the elderly in long-term care, those older than 85?years and those with dementia. Copyright (c) 2012 John Wiley & Sons, Ltd.