Early spontaneous gesture, specifically deictic gesture, predicts subsequent vocabulary development in typically developing (TD) children. Here, we ask whether deictic gesture plays a similar role in predicting later vocabulary size in children with Down Syndrome (DS), who have been shown to have difficulties in speech production, but strengths in spontaneous gesture and baby sign use. We compared the gestures and baby signs produced by twenty-three children with DS (Mage = 2;6) and twenty-three TD children (Mage = 1;6), in relation to their expressive spoken vocabulary size one year later. Children with DS showed significant deficits in gesture production, particularly for deictic gestures, but strengths in baby sign production, compared to their typically developing peers. More importantly, it was the baby signs produced by children with DS, but not deictic gestures, that predicted their spoken vocabulary size one year later. Our results further highlight the important role baby signs can play in language development in children with developmental disorders.