Researchers measured the safety performance of electronic health record (EHR) systems using simulated medication orders that can lead to adverse events or death in order to evaluate how well the systems identified these errors, and the mitigating effect of computerized physician order entry and clinical decision support (CDS) tools. Safety performance increased moderately over the 10-year study period but there was considerable variation in performance based on the level of decision support (basic or more complex) and EHR vendor; safety risks persist despite EHR implementation.