Several studies have shown unique morphological traits of sloths, affecting varied phenotypic traits from skeletal parts to soft tissues. Here we present the first descriptive allometric pattern of mandible form among the brown-throated sloth Bradypus variegatus (Schinz, 1825), based on the study of 25 specimens by means of geometric morphometric methods. The results obtained indicate that the species has a non-allometric slope, and therefore shape variation could hardly be explained by size. An established 'lever index', which can characterize the mandibular mechanical advantage, was maintained independently of the mandibular size. This non-geometric scaling of jaw form in sloth represents another uniqueness of this animal taxon.