Although the NHS operates throughout the United Kingdom, it is organised, and services are planned, differently in each of the four countries: England, Wales, Scotland and Northern Ireland. Curiously, the differences are generally either overlooked or dismissed as irrelevant. Yet their persistence gives the lie to the view that the NHS is a highly centralised, monolithic entity. Moreover, they illustrate the paradox of considerable diversity within a unitary state. This paper examines some of the variations that exist, noting that recent changes in the organisation of health services have done little to modify these differences. Indeed, in regard to developments in the private health sector and to approaches to planning and priority-setting, the differences may, in future, become greater. For such a compact entity, UK policy analysts are surprisingly uninformed about practices occurring around them. The paper argues that there is a need for researchers and policymakers to pay more attention to intra-UK variations such as those evident in the NHS and to devise ways of ascertaining their impact on service delivery and, if possible, on performance.