Objective: We examine the ways that romantic relationship biographies are related to whether, how, and with whom individuals complete advance care planning (ACP), preparations for end-of-life medical care. Method: Data are from an Internet survey of 2,144 adults aged 18 to 64, all of whom were either married to or cohabiting with an opposite-sex partner. Results: Cohabitors were less likely than married people to complete ACP. Relationship quality was an important influence on ACP, but did not account for the differences between married and cohabiting persons. Differences were largely explained by the age composition of the groups. Discussion: Couples who foresee a long and stable future together are those most likely to engage in end-of-life planning, a preventative health behavior with long-term consequences for well-being.