Open access. It is now 15 years since Bell and Redelemeier published their landmark study demonstrating higher mortality for people admitted to hospital during weekdays compared with the weekend.1 Examining the records of 3.8 million patients admitted over a 10-year period to emergency departments in Ontario, Canada, this ‘weekend effect’ existed over a range of acute conditions, including 23 out of the 100 leading causes of death. Since that paper in 2001, over 100 studies have explored the weekend effect, across a range of patient populations and health systems.2 Surprisingly, despite this large number of studies, there remains ongoing debate about whether the weekend effect exists, and if so, what causes it......