BackgroundIncreasing numbers of people will die with dementia, many in the acute hospital. It is often not perceived to be a life-limiting illness.AimsTo investigate the prevalence of dementia in older people undergoing emergency medical admission and its effect on outcomes.MethodLongitudinal cohort study of 617 people (aged over 70). The main outcome was mortality risk during admission.ResultsOf the cohort, 42.4% had dementia (only half diagnosed prior to admission). In men aged 70–79, dementia prevalence was 16.4%, rising to 48.8% of those over 90. In women, 29.6% aged 70–79 had dementia, rising to 75.0% aged over 90. Urinary tract infection or pneumonia was the principal cause of admission in 41.3% of the people with dementia. These individuals had markedly higher mortality; 24.0% of those with severe cognitive impairment died during admission (adjusted mortality risk 4.02, 95% CI 2.24–7.36).ConclusionsThe rising prevalence of dementia will have an impact on acute hospitals. Extra resources will be required for intermediate and palliative care and mental health liaison services.