The objective of this study was to examine the prevalence of potentially inappropriate medications (PIMs) and potential adverse drug effects (ADEs) in older adults presenting to the emergency department (ED). This was a prospective observational study of a convenience sample of adults 65 years and older presenting to the ED at an urban, tertiary care hospital. Potentially inappropriate medications were defined according to 2003 Beers criteria. Potential ADEs were defined as either (1) a potential drug-drug interaction, (2) alternative medication likely to cause toxicity or drug interactions, or (3) toxic doses of vitamins or minerals. Of 174 eligible patients, 124 were enrolled. The mean number of medications used per patient was 8.6 (range, 0-20). Thirty six patients (29%, 95% confidence interval, 27%-37%) presented to the ED with at least one PIM. Eight PIMs were prescribed in the ED, representing 16% of all prescriptions in the ED. Potential ADEs meeting the defined criteria were found in 26.6% of patients. A subanalysis of a random sample of charts revealed significant discordance between medication lists obtained by the research assistants and that of the health care providers. Older ED patients are at high risk for use of potentially inappropriate medications and ADEs. This problem may be magnified by inaccurate medication lists obtained by ED providers. A larger multicenter study may help to better define the scope of this problem.