A convincing body of literature demonstrates that adequate nurse staffing improves patient safety. However, achieving an appropriate nurse-to-patient ratio may necessitate using temporary staff, who may themselves be a source of error due to being unfamiliar with the care environment. This analysis of national MEDMARX data found that medication errors committed by temporary staff, primarily nurses, were more likely to cause patient harm than errors committed by regular staff. Although the findings may represent reporting bias, since MEDMARX consists of voluntarily reported data, prior studies have also demonstrated that high levels of temporary staff may pose patient safety risks.