The outcomes for those with dementia admitted to acute hospitals are often poor, with higher mortality, increased risk of institutionalisation and longer length of stay. The aim of this study was to examine the impact of dementia on length of stay and the associated cost of care in acute hospitals in Ireland. People with a recorded diagnosis of dementia were found to have a significantly longer length of stay than those with no recorded dementia. Multiplying the excess length of stay by the number of dementia-related admissions gave an estimate of 246,908 additional hospital days per annum due to dementia at an associated additional annual cost of over Euro199 million. Improving the experience of those with dementia in acute hospitals will likely lead to cost savings for the health service; however, it will require a number of measures including: earlier diagnosis, training for medical professionals and improvements in the built environment.