Advance directives (ADs) detail patients' end-of-life (EOL) care preferences. We estimated AD prevalence rates among a Medicare Supplement population and determined characteristics associated with having ADs. We also estimated the impact of having an AD on EOL Medicare expenditures among respondents who later died. Survey respondents with an AD (72%) were significantly more likely to be female, older, nonminority, higher income and education, and have more comorbid conditions. Following regression adjustments, EOL expenditures were significantly lower for those with ADs in the last 3 months (-US$11 189) and 1 month (-US$6092) prior to death. Patients with ADs specifying their wishes for EOL care had significantly lower medical expenditures during the last few months of life. However, disparities exist among those with ADs that may warrant interventions.