The role of social support networks in medication adherence among HIV-infected substance users remains understudied. In this secondary data analysis, the authors sought to determine the relationship between social support networks and antiretroviral adherence among HIV-infected substance abusers receiving methadone. They analyzed data collected in a 24-week study of 76 methadone-maintained, HIV-infected substance abusers randomized to directly observed antiretroviral therapy or treatment as usual. The authors used logistic regression to examine the relationship between social support networks and self-reported antiretroviral adherence. Their results showed that study participants had an average of 1.36 social network members (SD = 1.4); 34% of participants had at least one drug user and 25% had at least one HIV-infected person in their network. The presence of network drug users and HIV-infected network members was associated with less antiretroviral medication adherence (p < .05). The authors conclude that both social network density and characteristics of network members have implications for medication adherence.