In-hospital mortality for many conditions is higher on the weekends than on weekdays—a phenomenon known as the weekend effect. Some hypothesize lower specialty physician staffing levels on weekends explains the mortality difference. This cross-sectional study compared specialist staffing levels and mortality rates at 115 hospitals in the English National Health Service on Sundays compared to Wednesdays. Researchers found a higher mortality rate and lower intensity of specialty services on weekends, but there was no correlation between the two ratios. Although this study is not definitive, it does imply that alternate mechanisms may explain the weekend effect, such as case mix differences, variation in nonphysician staffing, or lower availability of diagnostic services. A previous PSNet interview discussed the weekend effect in health care.