This article compares the language profile of Italian pre-schoolers with Down syndrome (DS) and with Specific Language Impairment (SLI) matched on mental age. We analyzed the lexical and grammatical abilities in comprehension and production using different linguistic tasks. Results show that language profiles are very similar. No significant differences appear in the comprehension and in the production of lexicon. Also qualitative analyses of morphosyntactic errors reveal strong similarities between the two groups of children considered. Some differences between children with DS and SLI emerge in comprehension and production of grammar. Specifically, in respect to children with SLI, children with DS produce significantly more omissions and they show a Mean Length of Utterances - measured in a sentence repetition task - significantly shorter. The results are discussed taking into account the role of the cognitive abilities as well as the linguistic features of the Italian.