Changes in forest structure were examined 10–15 months after an unprecedented understorey wildfire burnt previously undisturbed primary forest in central Brazilian Amazonia, following the severe 1997–1998 El Niño dry season. On the basis of 20 0.25 ha plots (10 m×250 m) in both burnt and unburnt forest, we found marked differences in the overall live biomass, canopy openness and understorey vegetation. On average, 36% of all trees equal to or greater than 10 cm DBH were found to be dead in the burnt forest, and there was also a near-complete mortality in all pre-burn saplings. Using an allometric equation to predict biomass mortality we estimate that the tree mortality rates found would commit an additional 25.5 t C/ha to be released from these BFs. The dramatic increase of aboveground dead biomass in BF is of major global concern because of the increased flux of CO2 to the atmosphere, which has a role in enhancing the greenhouse effect and promoting climate change.