Second-order mental state attribution in two groups of children with non-specific intellectual disability and Down syndrome was investigated. The children were compared to overall mental age-matched group of typically developing children. The aim of the present study was to determine the specificity of the theory of mind deficit to different groups of children with intellectual disability. The results clearly showed that children with Down syndrome performed more poorly than the children with non-specific intellectual disability, and that typically developing children perform significantly better than do other groups. The findings are discussed in terms of the specificity of the etiology-related profiles of intellectually disabled groups. Several critical issues related to intervention strategies in the field of intellectual disability are also discussed, considering the educational practices.