Abstract Pediatric cancer affects >15,000 US children annually. Treatment advances have led to an increase in those surviving the disease, and these patients must be managed to control their long-term comorbidities. Unfortunately, a majority are nonadherent to post-treatment care guidelines and become lost to follow-up. This is especially true for those from underserved backgrounds, including survivors who are Black and Latine. To help understand this disparity, we studied the organization and delivery of pediatric cancer survivorship care at an urban comprehensive cancer center. Research included: 1) a qualitative study exploring healthcare barriers and facilitators of survivors’ adherence to long-term follow-up care, as determined by N=31 key informants (pediatric oncology care providers, administrators), and; 2) a retrospective cohort study (2007- 2020) among N>350 survivors (10% Black, 28% Latine, 12% Asian; 47% from vulnerable neighborhoods) assessing social determinants of health (SDoH) and its cofactors, adjusted for vital status. Interviews were recorded, transcribed, and thematically analyzed using software (K>.70). Three major themes emerged in survivors’ adherence: 1) healthcare system-level influences (69%), SDoH (25%), and intra/interpersonal factors (16%). At the system-level, informants noted opportunities to strengthen adherence, especially for survivors from underserved backgrounds, including the provision of greater social support (14%), easing appointment scheduling (11%), offering high-quality ambulatory and specialty care within the system upon entering young adulthood (12%), and cultural competency training for staff (6%). Among SDoH, informants noted transportation and geographic challenges in accessing the healthcare system (25%), insurance coverage for follow-up care (17%), and strengthening trust with marginalized communities (17%). For intra/interpersonal factors, time- and age-related changes in survivors’ medical needs were acknowledged as barriers to be overcome (28%), along with providing greater patient education (11%) and heightened salience of follow-up care (17%). Conversely, the provider-patient relationship was noted as a strength in promoting adherence (23%). Retrospective cohort results revealed that survivors’ attendance at dedicated clinics was suboptimal (52% >= 2 years off-therapy), as were rates of system-wide ambulatory care encounters 3+ and 5+ years post-therapy. At the bivariate level, non-Hispanic Black survivors (68%), adolescents (58%), and those with CNS tumors (81%) had the lowest likelihood of survivorship clinic attendance (p<.05)–underscoring qualitative findings on SDoH. Area-level SDoH indices were unrelated to the cohort’s adherence, highlighting qualitative findings on intra/interpersonal barriers and facilitators. These data lend insights into transformations possible within the organization and delivery of healthcare to young survivors, especially those from underrepresented backgrounds, including greater attention to SDoH and strengthening cultural competence among health system employees. Citation Format: Marcelo Sleiman Jr, Tara Suntum, Nina Kadan-Lottick, Brianna Miller, Mary R Yockel, Arnold Potosky, Chiranjeev Dash, Adil Alaoui, Burton Appel, Ken Tercyak. A mixed-methods health services analysis of disparities and social vulnerabilities in childhood cancer survivors’ long-term follow-up care [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr B067.