Within Asia, HIV prevalence is highest in Thailand, including thousands of children and adolescents. Care for children born with HIV [perinatal transmission of HIV (PHIV)] will need to focus on adolescents for the foreseeable future. Thai PHIV adolescents experience significant mental health and psychosocial challenges, including treatment adherence. Yet, few, if any, comprehensive interventions for them exist. CHAMP+, an evidence-based intervention adapted for Thailand, was evaluated with a pilot randomized control trial at four HIV clinics. Eighty-eight dyads of 9- to 14-year-old PHIV young adolescents/caregivers were randomized to CHAMP+ or standard of care (SOC). Eleven cartoon-based sessions were delivered over 6 months. Participants completed baseline, 6-month (postintervention), and 9-month surveys, measuring youth outcomes (e.g., mental health and adherence), contextual factors (e.g., demographics and caregiver factors), and self- and social-regulation factors (e.g., HIV knowledge and youth-caregiver communication). Multi-level modeling to account for clustering within individuals was used to assess longitudinal changes within and between groups. All families randomized to CHAMP+ completed the intervention. Although the study was not statistically powered to detect differences in treatment effects, the CHAMP+ group significantly improved at 6 months in youth mental health and adherence, HIV knowledge, youth-caregiver communication, internalized stigma, and HIV-related social support, with most improvements sustained at 9 months and significantly better improvements than the SOC group on a number of outcomes. High levels of baseline viral suppression highlight the importance of reaching these young PHIV adolescents at a period of lower risk before adherence and other challenges emerge. Designed to be delivered with limited cost/resources, CHAMP+ Thailand holds scale-up potential.