This case study shares the events of a near miss when a patient almost received a fatal dose of insulin in response to another patient's reported hyperglycemia. Ironically, the root cause of the problem involved a new bar-coding system to prevent errors in patient identification. The authors discuss the case in detail and advise caution in the implementation of new technology (eg, computerized provider order entry), which may solve safety issues but create the opportunity for others. This article is part of a special collection entitled "Quality Grand Rounds," a series of articles published in the Annals of Internal Medicine that explores a range of quality issues and medical errors.