Patients admitted on the weekend may be at increased risk for complications and mortality. This analysis of a large national database examined variations in outcomes following in-hospital cardiac arrest by day versus night and weekday versus weekend. The investigators found that return of spontaneous circulation for 20 minutes or longer, a positive outcome, was more likely during weekday business hours compared with nights or weekends. Similarly, survival to hospital discharge was worse on nights and weekends. These results are consistent with prior studies that demonstrated worse outcomes for patients admitted to hospitals during nights or weekends. Raising concerns that patients who had in-hospital cardiac arrest on nights or weekends might have been more ill at baseline, a related editorial encourages rigorous evaluation of any staffing changes meant to address the weekend effect.