The Adolescent Medicine Trials Network for HIV/AIDS Interventions is evaluating treatment adherence interventions (AI) to improve virologic suppression (VS) among youth with HIV (YWH). Using a microsimulation model, we compared two strategies: standard-of-care (SOC) and a hypothetical 12-month AI that increased cohort-level VS in YWH in care by an absolute ten percentage points and cost $100/month/person. Projected outcomes included primary HIV transmissions, deaths and life-expectancy, lifetime HIV-related costs, and incremental cost-effectiveness ratios (ICERs, $/quality-adjusted life-year [QALY]). Compared to SOC, AI would reduce HIV transmissions by 15% and deaths by 12% at 12 months. AI would improve discounted life expectancy/person by 8 months at an added lifetime cost/person of $5,300, resulting in an ICER of $7,900/QALY. AI would be cost-effective at $2,000/month/person or with efficacies as low as a 1 percentage point increase in VS. YWH-targeted adherence interventions with even modest efficacy could improve life expectancy, prevent onward HIV transmissions, and be cost-effective.