The fifth and final article in the series on patients with dementia in acute care examines challenging behaviour. Hospital admission, combined with unfamiliar surroundings and memory problems, can be frightening and disorientating for those with dementia. This can lead to behaviour which is perceived as 'disruptive' or 'difficult'. Aspects of the hospital environment or care practice can contribute to problems that may be misinterpreted and lead to challenging behaviour. Staff should seek to understand the cause of challenging behaviour, assess the possible causes and use strategies to reinforce familiarity and minimise distress for these patients.