Abstract: The use of temporary staff in healthcare is on the rise due in part to work-force shortages and perceived cost savings. They may present an increased risk of errors from insufficient training and orientation, and less familiarity with local culture and practice. However, their impact, particularly in the emergency department where the risk of preventable medication errors is high, has not been established. The objective of this study was to evaluate whether temporary staff medication errors would be associated with more severe harm than permanent staff medication errors. We used a national Internet-based medication error reporting system (MEDMARX) and did a cross-sectional study of the dataset between the years 2000 and 2005. After adjusting for clustering by facility, temporary staff errors were more likely than permanent staff errors to reach the patient (odds ratio [OR] 1.42, 95% confidence intervals [CI] 0.97–2.09), require patient monitoring (OR 1.91, 95% CI 1.21–3.03), result in temporary harm (OR 3.11, 95% CI 1.13–8.59), and be life-threatening (OR 8.63, 95% CI 1.22–61.0). In conclusion, emergency department medication errors associated with temporary staff were more harmful than those associated with permanent staff.