OBJECTIVES: The goal of this study was to evaluate the impact of electronic medical record (EMR) use on the frequency of visits due to an adverse event as reported in the National Ambulatory Medical Care Survey (NAMCS) 2007-2008 database. The specific objective was to determine the frequency of adverse events in patient visits that included the use of an EMR compared to visits without the use of an EMR. An adverse event was defined as an adverse outcome from medical or surgical care or an adverse drug event.  METHODS: The study design was a retrospective, cross-sectional, observational analysis of the NAMCS database from 2007-2008.  Patient visits that were the result of an adverse event were selected from all established patient visits. The frequency of adverse events was analyzed with respect to the use of an EMR. Patient visits were weighted with a statistical multiplier to generate national estimates.  RESULTS: An adverse event occurred in 44,035,493 (2.6%) patient visits. Of these visits, 26,067,600 (1.5%) did not include the use of an EMR, while 17,967,893 (1.1%) included use of an EMR. The majority of visits including the use of an EMR were by female patients (59.4%), white patients (83.2%), or patients age 45-64 years (29.2%). Only 40.2% of established patient visits included the use of an EMR.  CONCLUSIONS: Adverse event frequency was lower in patient visits that utilized an EMR as compared to patient visits that did not include the use of an EMR. Increasing EMR use will allow healthcare professionals to further prevent adverse events.