Background: Advance healthcare decision-making presumes that a prior treatment preference expressed with sufficient mental capacity ("T1 preference") should trump a contrary preference expressed after significant cognitive decline ("T2 preference"). This assumption is much debated in normative bioethics, but little is known about lay judgments in this domain. This study investigated participants' judgments about which preference should be followed, and whether these judgments differed depending on a first-person (deciding for one's future self) versus third-person (deciding for a friend or stranger) perspective.