DESCRIPTION (provided by applicant): There are low levels of continuity of HIV medical care and viral suppression and high rates of HCV among people who inject drugs (PWID). The proposed study is an RCT to improve health outcomes and reduce risk behaviors among HIV/HCV co-infected PWID and their social network members. The experimental condition is a small-group and dyadic based intervention to train HIV/HCV co-infected PWID in communication and adherence skills and to recruit their social networks for HIV/HCV testing and promote HIV medical care adherence, facilitate HCV treatment, and HIV/HCV risk reduction. The intervention will employ a mhealth approach to cue behaviors and address barriers to adherence. PWID will be trained to use mobile technology, specifically SMS, to promote testing and risk reduction to their social network members. The intervention is designed to be low cost, easily integrated into a variety of medical care settings. We propose recruiting 300 HIV/HCV co-infected PWID who have had an interruption in HIV care within the prior two years. Half will be randomly assigned to the experimental condition and half to the equal attention control. The experimental intervention will include 8 group sessions that focus on adherence skills and peer education, 2 dyad sessions with network members, monthly booster sessions for 6 months, and mhealth cuing of behavior for 6 months. These Index participants will be followed for 24 months (3, 6, 12, 18, & 24 month assessments) including biweekly assessments using personalized SMS (text messages to assess adherence to medical appointments and to cue skills for adhering to HIV medications). Control Indexes will also be followed for 24 months. Index participants will be linked to the Johns Hopkins HCV co-infection clinic to assess liver function and HCV chronicity. To assess HIV medication adherence, we will use surveys, plasma ARV assays, CD4 counts, viral load, and unannounced pill counts via SMS. Those meeting medical criteria will be offered HCV treatment. Additionally, 450 HCV positive network members will be recruited, tested for HIV and HCV, and followed longitudinally to examine the social diffusion of HCV/HIV treatment uptake, adherence, and risk reduction.