Background: It is generally assumed that children with Down syndrome (DS) present a deficit in lexical production relative to their cognitive abilities. However, the literature on this topic has recently shown several contradictory results. In addition, most studies only consider vocabulary production in its vocal modality. However it is also necessary to take into account gesture production, since this is a strength in children with DS. Our main purpose in this study, therefore, was to investigate the relationship between cognitive development and vocabulary size in both its vocal and gestural modalities in a broad sample of Spanish children with DS. Method: Participants in the study were 66 children with DS and 66 children with typical development (TD), with a mental age (MA) of 14-28 months (divided into five groups with a MA of 14-16, 17-19, 20-22, 23-25 and 26-28 months). Children were matched on the basis of their gender and MA. Productive vocabularies were collected using an adaptation of the MacArthur-Bates CDI for children with DS. Results: In vocal modality, the number of words produced by children with DS and children with TD is similar. As in previous studies, our data confirmed that gestural communication is superior in children with DS. However, when words and gestures are combined, the performance of both groups of children is practically equal. Conclusion: Our results do not support a specific dissociation between cognitive and lexical development in children with DS. (Contains 2 tables.)