System dynamics (SD) is an established simulation methodology used to explore the behaviour of social systems over time. The field has addressed challenging sustainability problems in fisheries, urban planning and environmental resource management. It has also been successfully applied to health care, in chronic disease modelling and workforce planning. This paper presents SD models of health-care sustainability, and illustrates two complementary applications of SD: (i) continuous simulation of health-care infrastructure adequacy; and (ii) conceptual modelling of the wider public policy context for health-care sustainability. The infrastructure model provides a simulator for evaluating impacts of population growth and ageing, as well as assessing the likely effects of policy interventions on system sustainability. This model is validated using empirical data from Irelandís public health service, and its practical application for sustainability analysis is illustrated. Our conceptual endogenous SD model explores a wider system boundary and public policy interdependencies that impact sustainability outcomes.