Background: Because of their difficulties in language development, various studies have focussed on the precursors of linguistic skills in children with Down syndrome. However, data on the predictive role of joint attention on language development in this population are inconsistent. The present study aimed to analyse attention behaviours in a group of children with Down syndrome. The existence of both concurrent and longitudinal relationships between joint attention and vocabulary development was investigated. Method: The participants were 18, 24-month-old, Italian children with Down syndrome. The children's attention skills were assessed during semi-structured free-play sessions in interaction with their mothers. A nominal exhaustive scheme was applied to code the children's behaviour. Moreover, the children's vocabulary development (both receptive and expressive) was assessed with the Italian version of the MacArthur-Bates Communicative Development Inventory at both 24 and 30 months. Results: Data analyses showed that children with Down syndrome spent a large part of the interactive play session in joint attention situations. Moreover, the children's behaviour of proposing a joint attention focus to their communicative partners appeared to be a significant predictor of the children's vocabulary comprehension skills as assessed 6 months later. Conclusions: These results support the hypothesis of continuity between preverbal precursors and vocabulary development in a population with atypical development.