Diet is among the ecological factors that explains the diversity of brain size in vertebrates. Research in phyllostomid bats —the family with the greatest trophic diversity among mammals— suggests that frugivorous species have comparatively larger brains than species from other trophic guilds. However, studies to date have focused on the relationship between diet and the brain as a whole. Whether diet affects the relative size of different brain regions remains unknown. This study examines for the first time the relationship between diet and the relative size of different encephalic structures that are involved in sensory ecology, memory and cognition in the family Phyllostomidae. Species that are mainly or strictly herbivorous have proportionally larger brain regions that are involved in spatial memory and olfaction than animalivorous species. In the latter, some brain regions that are responsible of visual and auditory integration are proportionally larger than in the former. The evolution of different feeding strategies may have driven changes in the dimensions of different brain regions and may help to understand the overall variation of brain size in the larger radiation of Neotropical bats.