Numerous dimensions of the peer social networks of children with Down syndrome were examined within a developmental framework. Results revealed that for many key measures, particularly involvement in play, linkages to other settings, and control of play, children with Down syndrome have less well-developed peer networks even in comparison to a mental age matched group of typically developing children. This suggests both an absence of any social advantage in the peer context for children with Down syndrome and the existence of unusual difficulties that may be traced to underlying problems in peer-related social competence. The need for future observational studies of peer interactions for this group of children was emphasized.