Significance: South Africa has the highest burden of perinatally HIV-infected children in the world with an estimated 320,000 HIV-infected children. The public sector is responsible for the care of the vast majority of these children and is poorly prepared to facilitate transition from pediatric to adult services, a process critical for achieving long-term treatment success in this vulnerable population. Quantitative studies to date involving HIV-infected adolescents who have transitioned to adult care are inadequate to address the challenges facing South Africa due to 1) small sample sizes and 2) exclusive enrollment of adolescents in resource-rich areas. Innovation: This study will be the first evaluation, to our knowledge, of transition outcomes for HIV-infected adolescents in sub-Saharan Africa. We will use a national database to evaluate the largest number of HIV- infected adolescents who transitioned to adult care thus far allowing for a robust analysis of factors affecting transition. The proposed research will develop a transition readiness score to assist clinicians and researchers. Approach: We will determine the following outcomes: vital status, loss to follow up, and virologic failure among ~800 urban, perinatally HIV-infected adolescents who have transitioned to adult care at Prince Mshiyeni Hospital outside of Durban, South Africa (Aim 1). We will use qualitative and quantitative methods to determine the psychosocial, clinical, and structural factors that facilitate or hinder successful transition to adult care (Aim 2). Using data from Aims 1 and 2, we will develop a transition readiness score to identify adolescents ready for transition to adult care and those who may require additional support prior to or during transitioning to adult care (Aim 3). Investigators: Brian Zanoni trained in Internal Medicine and Pediatrics with specialization in Infectious Disease and is a new investigator with extensive clinical experience in adolescent HIV care in South Africa, as well as a strong research foundation and ample mentorship. Mohindran Archary is a South African Pediatric Infectious Disease Specialist who oversees Prince Mshiyeni Hospital; he has been a co-investigator on several pediatric and adolescent studies in South Africa. Mahomed Yunus Moosa is a South African Adult Infectious Disease Specialist serving as the referral specialist for all of KwaZulu-Natal. In addition, he has valuable experience in HIV clinical research in South Africa. Marnie Vujovic is a South African clinical psychologist with considerable experience in the development and implementation of psychosocial programmes for children and adolescents infected with HIV. Jessica Haberer is an expert in pediatric and adult antiretroviral therapy adherence measurement and intervention in resource-limited settings and serves as Dr. Zanoni's mentor. Norma Ware is a medical anthropologist at Harvard Medical School with extensive experience in social and behavioral qualitative research on HIV treatment adherence and linkage to care in sub-Saharan Africa. Robert Parker is a senior biostatistician at with a wealth of experience in analysis involving HIV/AIDS research.