ABSTRACT: While the cultivation of conventional Bt corn has been widely adopted in Brazil, the production of Bt sweet corn is still incipient. The main lepidopteran pests found attacking conventional and sweet corn in Brazil are Spodoptera frugiperda (J.E. Smith) and Helicoverpa zea (Boddie). Additionally, a new harmful Lepidoptera species has recently appeared in Brazil, Helicoverpa armigera (Hübner). Since Bt sweet corn in Brazil is as yet cultivated on a limited scale there is no scientific information available about the performance of Bt sweet corn against lepidopterans out in the field. Thus, we conducted two field experiments to evaluate the efficacy of Bt sweet corn (event MON89034), alone and in conjunction with insecticides, against major lepidopteran pests found in midwestern Brazil (in the state of Goias). Both experiments followed a completely randomized block design (2 × 2 factorial) with two levels of sweet corn (Bt or conventional) crossed with two levels of insecticide (insecticide or no insecticide). The experimental treatments were replicated six times in each experiment. The results showed a slower advancing of defoliation caused by S. frugiperda in treatments with Bt corn. Likewise, less severe injury was observed on the corn ears (especially on the kernels) of Bt plants. The number of larvae (S. frugiperda and Helicoverpa spp.) sampled was also lower in the treatments with Bt corn. Overall, the application of insecticide did not increase the protection of Bt sweet corn and there was no significant difference in corn ear size and weight, nor in kernel yield, when comparing Bt and insecticide-sprayed plants.