Guided by the transtheoretical model of health behavior change, this study sought to explain why (a) rates of advance care planning remain low in the general population and (b) surrogate decision makers are often inaccurate about patients' end-of-life preferences. The study used quantitative data from a cross-sectional internet survey conducted between July and October 2010. The 2,150 participants aged 18-64 belonged to 1,075 married or cohabiting heterosexual couples. Participants included members of a nationally representative internet panel and a convenience sample from online advertisements. Older age was associated with a greater likelihood of having executed a living will and/or appointed a durable power of attorney for health care. Both older age and poorer health were independently associated with a greater likelihood of having discussed end-of-life health care treatment preferences. Completion of one's own end-of-life planning was unrelated to one's ability to accurately report one's partner's treatment preferences. Readiness to plan for end of life appears to differ across planning behaviors. Age and health are related to aspects of one's own advance care planning, but none of these factors are related to accuracy as a partner's surrogate.