PROJECT SUMMARY The transition from pediatric to adult care is an exceptionally precarious time in adolescent HIV care. Yet, little is known about which interventions might be most effective in supporting adolescents through this period. We will build on our well-established community-health platform and existing intervention research with adolescents living in Lima, Peru, to provide critical data on the effectiveness, cost, and implementation of a promising community-based differentiated care intervention that supports adolescents as they transition to adult HIV care. Our recent pilot study among a diverse group of 30 adolescents in Peru, the first of its kind in Latin America, demonstrated broadscale acceptability and convincing evidence of effectiveness with regard to outcomes of adherence, social support, self-efficacy and transition readiness. The intervention consists of stabilization of acute needs (e.g., housing instability or homelessness); health systems navigation to overcome administrative barriers to care (i.e., insurance changes, health center transfers); accompaniment to appointments in the adult clinic; social support groups; education and skills-building sessions; and mental health screening and referrals. The intensity of support and duration of the intervention (6 months or 12 months) will be differentiated based on patient-level factors such as adherence, viral load suppression, presence of familial support, and transition readiness. We will conduct a two-arm randomized clinical trial to determine the short- and long-term (i.e., post-intervention) efficacy of the intervention with regard to retention with viral load suppression as well as other indicators of well- being. We will compare the cumulative incidence of unsuccessful transition at 12- and 24-months, and stratify findings by the differentiated care pathway (i.e., the intensity of the intervention received). We will estimate the cost and cost-effectiveness of the study intervention in terms of cost per additional successful transition achieved. And, we will provide data on implementation considerations essential for uptake, sustainability, and successful adoption by the public sector. These include the reach of the intervention and the effectiveness and relative importance of each intervention component over the short and long-term. In pursuing these aims we will address a critical disparity of information with regard to interventions for adolescents living with HIV in the Latin American context.