Health care providers, hospital administrators, and politicians face competing challenges to reduce clinical errors, control expenditure, increase access and throughput, and improve quality of care. The safe management of the acutely ill inpatient presents particular difficulties. In the first of five Lancet articles on this topic we discuss patients' safety in the acute hospital. We also present a framework in which responsibility for improvement and better integration of care can be considered at the level of patient, local environment, hospital, and health care system; and the other four papers in the series will examine in greater detail methods for measuring, monitoring, and improving inpatient safety.