Second-order mental state attribution in 64 children with intellectual disabilities was investigated. Five second-order false belief tasks were administered to the participants. Significant differences were found between Down syndrome and non-specific intellectual disabled group on the tasks. Results contrast with the view that individuals with Down syndrome have an intact theory of mind and suggest that in their attributions of second-order mental states, children with Down syndrome perform worse than do other group of children with non-specific intellectual disabilities. The findings are discussed in terms of the specificity of the etiology-related profiles of ID groups, considering educational and social inclusion practices.