This study reports data from the National Electronic Injury Surveillance System, a representative sample of 63 hospitals that provide data on emergency department (ED) visits for injuries, poisonings, and adverse drug events (ADEs). Based on 2004-2005 data, the authors estimate that ADEs result in more than 700,000 ED visits yearly, most commonly due to allergic reactions or unintentional overdoses. ADEs were most common and most severe among the elderly, who were at significantly higher risk for both ED visits and hospitalization, confirming previous findings. As demonstrated in prior research, insulin and warfarin were the most common medications associated with ADEs requiring hospitalization. In this study, those drugs and digoxin accounted for nearly one-third of ADEs requiring hospitalization among the elderly. Thus, safety interventions targeting these medications could effectively reduce the burden of ADEs.