PURPOSE: Published data on outcomes among adolescents newly initiating antiretroviral treatment in the Latin American context are sparse. We estimated the frequency of sustained retention with viral load suppression (i.e., successful transition) and identified predictors of successful transition into adult care among youth (aged 14-21 years) with recently acquired HIV in Lima, Peru. METHODS: A retrospective cohort study was conducted among 184 adolescents and young adults who initiated antiretroviral therapy in an adult public sector HIV clinic between June 2014 and June 2019. Sustained retention (no loss-to-follow-up or death) with viral suppression was calculated for the first 12 and 24 months following treatment initiation. We conducted regression analyses to assess factors associated with successful transition to adult HIV care, including gender, age, occupation, nationality, pregnancy, same-sex sexual behavior, presence of treatment supporter, number of living parents, and social risk factors that may adversely influence health (e.g., lack of social support, economic deprivation). RESULTS: Patients were predominantly male (n = 167, 90.8%). Median age was 19 years (interquartile range: 18-21). Frequency of sustained retention with viral load suppression was 42.4% (78/184) and 35.3% (30/85) at 12 and 24 months following treatment initiation. In multivariable analyses, working and/or studying was inversely associated with successful transition into adult care at 12 months; number of known living parents (relative risk: 2.20; 95% confidence interval: 1.12, 4.34) and absence of social risk factors (relative risk: 1.68; 95% confidence interval: 0.91, 3.11) were positively associated with successful transition at 24 months. DISCUSSION: Sustained retention in HIV care was uncommon. Parental support and interventions targeting social risk factors may contribute to successful transition into adult HIV care in this group.