This case study shares the experiences of a patient who suffered a medication error in receiving a dose of insulin inadvertently. The author reviews the epidemiology of medication errors and adverse drug events and shares a systems approach to medication errors, the role individuals and the system played in this particular case, and the potential prevention strategies to be considered. Finally, a comment about the institution's response to the event is presented to illustrate the importance of bridging what happens at the bedside with what needs to happen from the executive suite. This article is part of a collection entitled "Quality Grand Rounds," a series published in the Annals of Internal Medicine that explores quality issues and medical errors.