The Rio+20 United Nations Conference on Sustainable Development represents a crucial opportunity to place environmental health at the forefront of the sustainable development agenda. Billions of people living in low- and middle-income countries continue to be afflicted by preventable diseases due to modifiable environmental exposures, causing needless suffering and perpetuating a cycle of poverty. Current processes of economic development, while alleviating many social and health problems, are increasingly linked to environmental health threats, ranging from air pollution and physical inactivity to global climate change. Sustainable development practices attempt to reduce environmental impacts and should, in theory, reduce adverse environmental health consequences compared to traditional development. Yet these efforts could also result in unintended harm and impaired economic development if the new "Green Economy" is not carefully assessed for adverse environmental and occupational health impacts. The environmental health community has an essential role to play in underscoring these relationships as international leaders gather to craft sustainable development policies.