Checklists have resulted in some of the most prominent successes of the patient safety movement, and the resulting publicity has led to wider implementation of checklists in a variety of care settings. This rapid dissemination of checklists has been accompanied by cautionary notes from those who have examined successful checklist-based interventions, who stress the importance of safety culture and other factors in ensuring intervention success. This systematic review of nine published studies of checklists also strikes a cautionary note, finding only moderate evidence that checklists are associated with safety improvements and noting significant methodological weaknesses in the existing literature base. Checklists are a powerful improvement tool, but as this study highlights, their success is often dependent on other interventions.