$BACKGROUND$: There is continuing public debate about treatment preferences at the end of life, and the acceptability and legal status of treatments that sustain or end life. However, most surveys use binary yes/no measures, and little is known about preferences in neurological disease when decision-making capacity is lost, as most studies focus on cancer. This study investigates changes in public preferences for care towards the end of life, with a focus on measures to sustain or end life.

$METHODS$: Large-scale international public opinion surveys using a six-stage patient vignette, respondents chose a level of intervention for each stage as health and decision-making capacity deteriorated. Cross-sectional representative samples of the general public in Great Britain and the USA (N = 2016). Primary outcome measure: changes in respondents' preferences for care, measured on a four-point scale designed before data collection. The scale ranged from: maintaining life at all costs; to intervention with agreement; to no intervention; to measures for ending life.

$RESULTS$: There were no significant differences between GB and USA. Preference for measures to sustain life at all costs peaked at short-term memory loss (30.2%, n = 610). Respondents selecting 'measures to help me die peacefully' increased from 3.9% to 37.0% as the condition deteriorated, with the largest increase occurring when decision-making capacity was lost (10.3% to 23.0%). Predictors of choosing 'measures to help me die peacefully' at any stage were: previous personal experience (OR = 1.34, p<0.010), and older age (OR = 1.09 per decade, p<0.010). Negative predictors: living with children (OR = 0.72, p<0.010) and being of "black" race/ethnicity (OR = 0.45, p<0.001).

$CONCLUSIONS$: Public opinion was uniform between GB and USA, but markedly heterogeneous. Despite contemporaneous capacitous consent providing an essential legal safeguard in most jurisdictions, there was a high prevalence of preference for "measures to end my life peacefully" when decision-making capacity was compromised, which increased as dementia progressed. In contrast, a significant number chose preservation of life at all costs, even in end stage dementia. It is challenging to respect the longstanding values of people with dementia concerning either the inviolability of life or personal autonomy, whilst protecting those without decision-making capacity.