Tehran University of Medical Sciences Journal of Modern Rehabilitation 2538-385X 17 2 2023 01 03 134 141 Monireh Aminian Department of Linguistics, Faculty of Literature, Humanities and Social Sciences, Sciences and Research Branch, Islamic Azad University, Tehran, Iran. Mahnaz Karbalaei Sadegh Department of Linguistics, Faculty of Literature, Humanities and Social Sciences, Sciences and Research Branch, Islamic Azad University, Tehran, Iran. Masoomeh Salmani Department of Speech and Language Therapy, Neuromuscular Rehabilitation Research Center, Semnan University of Medical Sciences, Semnan, Iran. Ali Jafari Naeemi Student research and Technology Committee, Semnan University of Medical Sciences, Semnan, Iran. 2021 08 09 2021 10 30 Introduction: Down syndrome (DS) as a chromosomal abnormality has different symptoms including cognitive problems and language delay. Studies showed a heterogeneous profile of language skills in this group of children. This study aimed to provide further information about the most vulnerable area of language -grammatical skills- regarding the unanalyzable utterances, clauses, phrases, grammatical morphemes, and mean length of utterances (MLU) in children with DS and compare them with those of non-verbal age-matched controls. Materials and Methods: The grammatical structures of 12 children with DS (non-verbal age=39 months) were compared to those of 50 non-verbal mental age-matched controls (non-verbal age=41 months). Clause, phrase, and grammatical morphemes were investigated through spontaneous language sample analysis according to Persian-language assessment remediation and screening procedure (P-LARSP). Results: Children with DS had higher percentages of unanalysable text units compared with typically matched peers (P≤0.001). The MLU, number of phrases and clauses structures, and inflectional morphemes were significantly lower in children with DS compared with typical children (P<0.001). Conclusion: Children with DS showed a noticeable gap in grammatical structures compared with typical children. The possibility of specific language problems in children with DS should be considered by future studies. https://jmr.tums.ac.ir/index.php/jmr/article/view/519