Numerous studies with general circulation models suggest that tropical deforestation can result in regional-scale climate change; namely, increased air temperature and wind speed and reduced precipitation and relative humidity. To quantify how this climate change should affect fire risk, we used the National Center for Atmospheric Research (NCAR) CCM3.2 general circulation model and remote sensing to estimate the effect of tropical deforestation on fire risk through the McArthur forest fire danger index (FFDI). Deforestation reduced precipitation and relative humidity and increased wind speed in the Amazon, Congo, and Indonesia/New Guinea. FFDI increased by 41, 56, and 58% in these three regions, respectively, primarily owing to higher wind speeds and reduced precipitation. Actual fire occurrence in the Amazon, as determined from NOAA-12 images, was strongly correlated with the FFDI calculated from meteorological data (P ≪ 0.0001). Using the observed relationship between FFDI and fire occurrence, we estimate increases in fire frequency of 44, 80, and 123%, in the Amazon, Congo, and Indonesia, respectively, with deforestation. In all three regions the largest relative increases in fire risk occurred in the more humid areas with the lowest original fire risk.