Variations in health care use within a country are complicated. In some cases they may reflect differences in health needs, in patient preferences or in the diffusion of a therapeutic innovation; in others they may not. There is evidence that some of the observed variations are unwarranted, signalling under- or over-provision of health services, or both. This study documents geographic variations for high-cost and high-volume procedures in select OECD countries. It finds that there are wide variations not only across countries, but within them as well. A mix of patient preferences and physician practice styles likely play an important part in this, but what part of the observed variations reflects over-provision, or whether there are unmet needs, remain largely unexplained. This report helps policy makers better understand the issues and challenges around geographic variations in health care provision and considers the policy options.