OBJECTIVES: Adverse drug events (ADE) in the elderly are important sequelae of drug treatment playing a role in non-adherence and increased hospitalizations and emergency visits.  This study sought to describe the rate of ADEs in an elderly population and to compare the characteristics of those who experienced ADEs to those who did not. METHODS: This study was a retrospective cross-sectional analysis that used a 10% random sample of the IMS LifeLink Health Plans commercial claims data during the period January 1,2001 through December 31, 2009.  Subjects had to be at least 65 years of age and have had at least one year of continuous medical coverage.  ADEs were defined based on previously published schema using ICD-9-CM codes that mention drug therapy or "due to drug" or "drug induced". ADEs occurring in hospitalizations, emergency department visits, and outpatient physician visits are reported.  Demographics, comorbidity, and health resource use were compared between persons with one or more ADEs compared to those without an ADE. RESULTS: