Few studies have been done on the quantification of stand-level leaf herbivory in tropical forests. We evaluated the significance of annual leaf loss due to folivorous insects on the calculation of aboveground net primary production (ANPP) in tropical rain forests along broad climatic and edaphic gradients on Mt. Kinabalu, Borneo. We estimated insect folivory at the stand level as the product of a lifetime leaf loss ratio and annual leaf production in the stand. We defined the lifetime leaf loss ratio as the ratio of litter-leaf mass consumed by folivorous insects to the total litter-leaf mass at the stand level. The lifetime leaf loss ratio ranged from 1.6 to 8.4 %. The annual leaf loss caused by folivorous insects ranged from 0.01 to 0.38 Mg C ha-1 year-1, or from 1.2 to 5.9 % of ANPP in these tropical rain forests. Our method of estimating folivory (1) simultaneously considers all the tree species, canopy layers, and species of folivorous insects, (2) avoids underestimating leaf herbivory due to the resorption of mobile organic and inorganic matter from senescent leaves at the time of leaf abscission, and (3) can readily be applied in forests elsewhere. © 2012 The Japanese Forest Society and Springer.