Tropical rainforests are often referred to as the lungs of the planet for their crucial role in the global carbon cycle. They also harbour a large proportion of the world’s biodiversity and provide commodities for consumers around the globe. But the health of these forests is declining due to logging, climate change, invasive species, and other impacts arising from human activities. Metaphorically speaking, decades of chain smoking are starting to take a big toll on this vital organ. Now there is a need for a suitable health care plan. The latest special issue of Science was dedicated to forest health. It reviews the present and future threats to tropical and temperate forests. Of particular interest is the growing research on tropical secondary forests and their capacity to sustain biodiversity and ecosystem services.