Accurate understanding of end-of-life terminology is essential to communications regarding end-of-life treatment preferences. This study was undertaken to assess the level of understanding of commonly used end-of-life medical terms among emergency department (ED) patients and visitors. In this prospective survey study, an oral structured interview was conducted in a university emergency department in 2008. Participants were asked to define 10 terms. Free text responses were scored by three investigators, using a health literacy 3-point scale (correct, partially correct, or incorrect). Among 303 participants (82% participation rate), 7.3% correctly defined 7 or more of 10 end-of-life terms. Terms most commonly understood included do not resuscitate (DNR) (56.3% correctly defined), ICU (51.8%), and durable power of attorney for health care (39.8%). Terms least correctly defined included resuscitation (15.3% correctly defined), physician-assisted suicide (9.4%), and euthanasia (7.4%). Factors associated with differences in accuracy in defining terms included age (age group 51–65 years had the highest accuracy), ethnicity (Caucasians had the highest accuracy), education (more education correlated with higher accuracy), and gender (females had higher accuracy). Income and personal advance directives were not associated with accuracy. A minority of participants (31%, n = 95) had previously completed an advance directive for themselves. In conclusion, ED patients and visitors demonstrated low levels of understanding of commonly used end-of-life medical terms. A minority of ED patients and visitors have completed advance directives. Completion of a personal advance directive does not correlate with an increase in knowledge of end-of-life terminology.