Temporary nurses are frequently used by hospitals to cover unexpected staffing shortages. Although the overall level of nurse staffing is clearly tied to patient safety, prior research has not found a link between the proportion of temporary nurses and patient care outcomes. This study, based on a database of 286 nursing units, also found that patient safety outcomes were not affected when levels of temporary staffing were low (less than 15% of total nursing hours). However, both patient falls and injuries among nurses increased with higher levels of temporary staffing. Based on these results, the authors argue that hospitals should use the 15% proportion as a benchmark for appropriate use of temporary nurses.