Bar code technology has been widely recommended to reduce adverse drug events (ADEs) by ensuring the correct medication and dose are dispensed, but prior research has pointed out potential unintended consequences of its use. This AHRQ–funded study measured the incidence of drug dispensing errors and potential ADEs before and after implementation of bar code–assisted dispensing at an academic hospital. Both types of errors were significantly reduced when each dose of medication was scanned, but potential ADEs were increased in a configuration requiring scanning of only one dose per batch. The authors conclude that bar coding systems should be configured to mandate scanning of each dose at least once during the dispensing process.