The weekend effect (higher mortality for patients in acute care settings on weekends compared to weekdays) has led to widespread concerns about hospital staffing. This retrospective study examined whether mortality for emergency admissions at four hospitals in the United Kingdom differed on weekends compared to weekdays. Unlike prior studies of the weekend effect, this study included multiple specific markers of patients' illness severity as well as hospital workload. Investigators found higher mortality associated with being admitted to the hospital during weekends compared to weekdays, but a significant proportion of the observed weekend effect was explained by severity of patient illness. They used three measures to approximate hospital workload: total number of admissions, net admissions (subtracting discharges from admissions), and percentage of beds occupied. None of these workload measures was associated with mortality. The authors conclude that differences in illness severity rather than health care team staffing explain the weekend effect. A recent PSNet interview discussed the weekend effect in health care.