Based on the first record in the state of Morelos and a new record for the Estado de México, we suggest that Reithrodontomys microdon preferentially uses an arboreal habitat. Specimens described here, for the most part (75%), were captured >4 m above ground on trees. Although historical records indicate that R. microdon is rare, our data may suggest otherwise. Assuming this species is preferably arboreal and that most inventories of rodents have focused on the ground, it is evident that, historically, this species has not been surveyed in its preferred habitat.