Brazil's comprehensive HIV treatment program does not specifically address ART adherence challenges for adolescents-a group accounting for the largest number of incident HIV infections in Brazil. We conducted three focus groups with 24 adolescents (age 15-24) living with HIV in Rio de Janeiro, separately for cisgender men who have sex with men, heterosexual-identified cisgender men and women, and transgender women of any sexual orientation, and key informant interviews (n = 7) with infectious disease specialists and HIV/AIDS service organization staff. Content analysis identified socioecological barriers and facilitators to adherence, including individual (e.g., low knowledge, side effects, and substance use), interpersonal (e.g., stigma from partners and health care providers) and structural (e.g., transportation and medication access) barriers. Overlapping and unique barriers emerged by sexual/gender identity. A community-informed, theory-driven ART adherence intervention for adolescents that is organized around identity and leverages social networks has the potential to improve HIV treatment and health outcomes for Brazilian adolescents.