Mitigating climate change presents unrivalled opportunities for improving public health. The policies that need to be implemented to reduce greenhouse gas emissions will also bring about substantial reductions in heart disease, cancer, obesity, diabetes, road deaths and injuries, and air pollution. The health benefits arise because climate change policies necessarily impact on two of the most important determinants of health: human nutrition and human movement. Although the health co-benefits of climate change policies are increasingly recognised by health professionals they are not widely appreciated by those responsible for policy. Because the existence of important health co-benefits will dramatically reduce the cost to society of taking strong action to mitigate climate change, failure to appreciate their importance could have serious environmental consequences. Health professionals have an urgent responsibility to ensure that the health benefits of environmental policies are understood by the public and by policymakers.