PURPOSE: Youth living with HIV (YLHIV) in the United States (U.S.) account for nearly one-third of new HIV infections and face significant barriers to care engagement; only 25% are virally suppressed. Healthcare transition (HCT) from pediatric/adolescent to adult-oriented care can be particularly disruptive. Accordingly, we prospectively examined HCT processes at 14 distinct geographical sites across the U.S. METHODS: We collected Audio Computer-Assisted Self-Interviews data and abstracted electronic medical records from 135 HCT-eligible YLHIV at baseline and 9-month follow-up. Descriptive analyses and multilevel modeling were conducted. Data also included qualitative interviews with 28 adolescent and 30 adult providers across 14 adolescent and 20 adult clinics, respectively. Interviews were analyzed using the constant comparative method; this analysis focused on specific HCT recommendations. RESULTS: At baseline, youth were primarily age 24 (78.8%), male (76.8%), black (78.0%), identified as a sexual minority (62.9%), had attended an HIV appointment in the past 3 months (90.2%), had Medicaid for insurance (65.2%), and were always or mostly always adherent to their antiretroviral therapy (65.9%). At the 9-month follow-up only 37% of YLHIV successfully transitioned to adult care. Both individual-level (insurance status and disclosure-related stigma) and clinic-level (adolescent clinic best practices) factors were significant. Adolescent and adult clinic staff offered recommendations to support HCT; these focused primarily on clinical changes. CONCLUSIONS: This study highlights the complex set of individual- and clinic-level factors associated with HCT. Addressing these key factors is essential for developing streamlined, comprehensive, and context-specific HCT protocols to support continuous care engagement for YLHIV.