The global HIV burden among adolescents ages 10-19 is growing. This population concurrently confronts the multifaceted challenges of adolescence and living with HIV. With the goal of informing future interventions tailored to this group, we assessed sexual activity, HIV diagnosis disclosure, combination antiretroviral therapy (cART) adherence, and drug use among adolescents living with HIV (ALHIV) in Lima, Peru. Adolescents at risk or with a history of suboptimal cART adherence completed a self-administered, health behaviors survey and participated in support group sessions, which were audio recorded and used as a qualitative data source. Additionally, we conducted in-depth interviews with caregivers and care providers of ALHIV. Thematic content analysis was performed on the group transcripts and in-depth interviews and integrated with data from the survey to describe adolescents' health related behaviors. We enrolled 34 ALHIV, of which 32 (14 male, 18 female, median age 14.5 years) completed the health behavior survey. Nine (28%) adolescents reported prior sexual intercourse, a minority of whom (44%) reported using a condom. cART adherence was highest in the 10-12 age group with 89% reporting ≤2 missed doses in the last month, compared to 36% in adolescents 13 years or older. Over 80% of adolescents had never disclosed their HIV status to a friend or romantic partner. Adolescents, caregivers, and health service providers described sexual health misinformation and difficulty having conversations about sexual health and HIV. In this group of ALHIV, adherence to cART declined with age and condom use among sexually active adolescents was low. Multifactorial interventions addressing sexual health, gaps in HIV-related knowledge, and management of disclosure and romantic relationships are urgently needed for this population.