This paper uses a difference-in-difference style estimation strategy to test separately the impact of competition from public sector and private sector hospitals on the efficiency of public hospitals. Our identification strategy takes advantage of the phased introduction of a recent set of substantive reforms introduced in the English NHS from 2006 onwards. These reforms forced public sector health care providers to compete with other public hospitals and eventually to face competition from existing private sector providers for care delivered to publicly funded patients. In this study, we measure efficiency using hospitals’ average length of stay (LOS) for patients undergoing elective surgery. For a more nuanced assessment of efficiency, we...