This article compared the language profiles of adolescents with Down syndrome (DS) and children with specific language impairment matched for nonverbal cognitive ability, and investigated whether similar relationships could be established between language measures and other capacities in both groups. Language profiles were very similar: Expressive language was more affected than language comprehension, and grammar was more affected than vocabulary in both domains. Both groups were impaired on tests of grammatical morphology and phonological memory. There were some differences between the groups, but these could be attributed to other features of development of people with DS.