Mexico is the third Latin American country with the most children and adolescents living with human immunodeficiency virus (ALHIV). There is a lack of information on the characteristics of this population. We aimed to describe the social and mental health characteristics of Mexican ALHIV. A census was conducted of all adolescent patients with HIV at a pediatric hospital ( n = 47; mean age 14.39, S.D. = 3.65) and their caregivers. We collected data on socio-demographic characteristics, family, intelligence, mental health, adverse life events, substance use, treatment, knowledge of Antiretroviral Treatment (ART) and HIV, and biomarkers. Most cases were transmitted vertically and self-reported ART adherence was above 90%. Some obstacles to adherence were medicine discomfort, believing that they did not need it, and forgetfulness. The vulnerabilities were intellectual disability, adverse life events, possible mental health problems, and little knowledge of their illness and treatment. These findings suggest the importance of interventions to improve the perception and knowledge of HIV and ART to increase ART adherence.