BACKGROUND: Public health must continually respond to new threats reflecting wider societal changes. Ecological public health recognizes the links between human health and global sustainability. We argue that these links are typified by the harms caused by dependence on private cars. METHODS: We present routine data and literature on the health impacts of private car use; the activities of the ‘car lobby’ and factors underpinning car dependence. We compare these with experience of tobacco. RESULTS: Private cars cause significant health harm. The impacts include physical inactivity, obesity, death and injury from crashes, cardio-respiratory disease from air pollution, noise, community severance and climate change. The car lobby resists measures that would restrict car use, using tactics similar to the tobacco industry. Decisions about location and design of neighbourhoods have created environments that reinforce and reflect car dependence. Car ownership and use has greatly increased in recent decades and there is little public support for measures that would reduce this. CONCLUSIONS: Car dependence is a potent example of an issue that ecological public health should address. The public health community should advocate strongly for effective policies that reduce car use and increase active travel.