The weekend effect of worse patient outcomes when admissions or procedures occurred outside of usual business hours has been documented across multiple care settings. In this analysis of pooled hospital administrative data across four countries, in-hospital mortality within 30 days of admission or surgical procedure was higher for patients admitted from the emergency department or undergoing interventions during the weekend, although there were specific differences by country. This consistency suggests that challenges with current weekend structure at hospitals should be examined across a broad range of clinical services and delivery models. An accompanying editorial suggests that the existence of the weekend effect is no longer in dispute and urges efforts toward identifying and addressing its underlying causes.