Studies examining the visual and verbal metaphorical comprehension of individuals with non-specific intellectual disability (NSID) are remarkably scarce; to date only one case study examined comprehension of metaphors in an individual with Down syndrome (DS). The current study explored both the understanding of conventional and novel metaphors and the comprehension of visual metaphors in individuals with NSID (aged 15-59, N = 53) and individuals with DS (aged 15-52, N = 50). Both etiology groups showed poor understanding of verbal and visual metaphor comprehension with worse performance on the visual task. However, the comprehension of novel metaphors was significantly higher than the comprehension of conventional ones, in both groups. As expected, individuals with DS understood fewer conventional metaphors than individuals with NSID, probably due to the linguistic deficiency characterizing individuals with DS. These findings were explained in light of the delay in linguistic ability that characterizes individuals with DS as well as the gradual expansion of their mental lexicon with increasing age.