Few studies have examined the current social relationships of injecting drug users. This paper examines the structural and relationship characteristics of the social networks of injecting drug users, and the relation of social network characteristics to the HIV infection risk behavior of frequency of injecting heroin and cocaine. The study sample was comprised of 293 inner city injecting drug users in Baltimore, Maryland. Most participants (89%) reported at least one family member in their social network, and 44% listed their mother or step-mother in their network. Presence of family members in personal social networks was not related to patterns of drug use examined here; however, those who reported a partner in their personal social network injected significantly less often than those who did not report a partner. Network density and size of drug subnetworks were positively associated with frequency of drug injection. The results of this study suggest that social network analysis may be a useful tool for understanding the social context of HIV/AIDS risk behaviors.