ABSTRACT Russia is one of five countries that account for the greatest number of infections in the world. Although historically associated with drug injection, Russia’s HIV epidemic is now primarily sexual, with a large number of infections among MSM. With few supports for medical care engagement, most HIV-positive MSM in Russia have unsuppressed viral load, fueling high continued disease transmission and poor health outcomes. HIV care engagement, adherence, and psychosocial coping are better among persons with supportive social resources. Given the hostile social circumstances they face, improved social supports are critical for the medical care engagement and psychosocial adjustment of HIV-positive MSM in Russia. This study will test an approach to help out-of-care, HIV-positive MSM identify, access, and mobilize social resources to support HIV care engagement. The mixed-methods research will begin with a formative phase of in-depth interviews with 25 PLH MSM in St. Petersburg as well as one supportive resource network member in the life of each participant to characterize the kinds of social resources that can be harnessed to support HIV care. Formative data and input from the study’s Community Advisory Panel will inform the tailoring of an intervention that has already been successfully pilot tested. The intervention study will recruit 100 out-of-care HIV+ MSM in community settings and online. After completing baseline assessments, participants will be randomized to either an individual care counseling (ICC) comparison condition or ICC plus a social support mobilization (SSM) intervention. In it, PLH MSM will attend five main and two booster sessions that underscore the benefits of medical care engagement, counter the effects of internalized intersectional stigma and promote resilience, and help participants develop and mobilize social resources supportive of HIV care. Support mobilization will begin by assisting participants develop care-supportive bonds with other group members, PLH friends, and connections made with LGBT and PLH NGOs. They will also be guided in developing and expanding supportive links with affirmative friends, family members, and other resources. In this way, the intervention will bolster care-related social support resources, resilience, and feelings of self-worth. Assessments administered at baseline will be repeated 6 and 12 months post-intervention, and in-depth followup interviews will be conducted with a subset of 20 participants to elicit feedback about the intervention experience. We hypothesize that the SSM intervention will produce greater preliminary evidence of benefit on the primary outcome of medical care attendance in the past 6 months and on secondary outcomes of having undetectable viral load, ART adherence, and psychosocial well-being. We will explore whether care-related outcomes are mediated by increases in social resources and other factors. If there is evidence of benefit, the intervention will be o...