Patients admitted to hospital with an acute medical emergency at weekends apparently have a higher rate and risk of complications and death than patients admitted on weekdays. In separate studies, a more favourable ratio of specialists to patients appears to be associated with improved outcomes. Combining these two findings, the HiSLAC project will test the theory that increasing the amount of specialist clinical care provided at the weekend will improve patient outcomes to a level comparable with those admitted on weekdays. We refer to high-intensity specialist-led acute care as HiSLAC. At the end of the HiSLAC project, we will be able to show: whether care at the weekends is better in hospitals with HiSLAC, whether the differences in outcomes between weekdays and weekends is less in hospitals with HiSLAC, and whether HiSLAC is cost-effective.