This study analyzed nearly 4 million consecutive hospital admissions in Ontario, Canada, over a 10-year period to determine whether mortality rates differed on weekends when staffing levels tend to be lower. Investigators discovered higher rates of in-hospital mortality for patients admitted with ruptured aortic aneurysms, acute epiglottitis, and pulmonary embolism. Of the 100 most frequent causes of death, 23 were associated with higher mortality when those patients were admitted on a weekend. While past research suggested that hospitals function less effectively during weekend hours, a notion supported by the Sunday night death of Libby Zion that raised questions about under-supervised residents, this study was the first to confirm the potential impact weekend staffing issues may generate on the quality and safety of inpatient care.