In this paper, I explore one way to bring bioethics and environmental ethics closer together. I focus on a question at the interface of health, sustainability, and justice: How well does a society promote health with the use of no more than a just share of environmental capacity? To address this question, I propose and discuss a mode of assessment that combines a measurement of population health, an estimate of environmental sustainability, and an assumption about what constitutes a fair or just share. This mode of assessment provides an estimate of the just and sustainable life expectancy of a population. It could be used to monitor how well a particular society promotes health within just environmental limits. It could also serve as a source of information that stakeholders use when they deliberate about programs, policies, and technologies. The purpose of this work is to focus attention on an ethical task: the need to fashion institutions and forms of life that promote health in ways that recognize the claims of sustainability and justice.