Poor adherence to antiretroviral therapy (ART) contributes to disease progression and emergence of drug-resistant HIV in youth with perinatally acquired HIV infection (PHIV +), necessitating reliable measures of adherence. Although electronic monitoring devices have often been considered the gold-standard assessment in HIV research, they are costly, can overestimate nonadherence and are not practical for routine care. Thus, the development of valid, easily administered self-report adherence measures is crucial for adherence monitoring. PHIV+youth aged 7-16 (n = 289) and their caregivers, enrolled in a multisite cohort study, were interviewed to assess several reported indicators of adherence. HIV-1 RNA viral load (VL) was dichotomized into >/≤ 400 copies/mL. Lower adherence was significantly associated with VL >400 copies/mL across most indicators, including ≥ 1 missed dose in past seven days [youth report: OR = 2.78 (95% CI, 1.46-5.27)]. Caregiver and combined youth/caregiver reports yielded similar results. Within-rater agreement between various adherence indicators was high for both youth and caregivers. Inter-rater agreement on adherence was moderate across most indicators. Age ≥ 13 years and living with biological mother or relative were associated with VL >400 copies/mL. Findings support the validity of caregiver and youth adherence reports and identify youth at risk of poor adherence.