OECD economies are undergoing a seemingly inevitable process of population ageing that has been changing income and consumption patterns. Notably, the demand for health services is expected to increase, while labour forces are projected to shrink. Both factors are projected to negatively impact the sustainability of health systems – the former through an increase in government expenditures on health and the latter through a decrease in government revenues. As health systems and their funding streams tend to be at least partially decentralised in most OECD countries, this fiscal pressure is expected to be asymmetric across levels of government. The objective of this paper is to provide order-of-magnitude estimates of the possible effects of population ageing on government finances across OECD countries, and to discuss reforms to fiscal federalism and intergovernmental relations with the purpose of funding expenditures at all levels of government.