We assessed the impact of forest fire on the nesting success of the endemic Red-knobbed Hornbill Aceros cassidix in north Sulawesi, Indonesia. Pre- and post-fire breeding activity was monitored at 60 nest trees. Low rainfall and possible reductions in fruit abundance did not appear to have an effect on initial nest uptake or on subsequent chick production at non-burnt nests, which were comparable to previous years. However, there was an adverse effect on productivity at nests that directly experienced fire and the accompanying heat and smoke in the vicinity, resulting in a post-fire nest success (62%) that was significantly lower than in previous years (78.6-80%). Population recruitment dropped by an estimated 47% to 0.17 fledglings/breeding pair. Our data suggest that, given the reproductive profile of this species and the ability of fire to reinforce its own negative effects on forest habitats, Red-knobbed Hornbill populations may be vulnerable to the potential effects of repeated fires. © Birdlife International 2000.