OBJECTIVES: This study addresses the challenge of improving outcomes for the 5% of individuals with complex chronic diseases who utilize 50% of health care resources. Previous interventions targeting this population have shown limited impact, often due to transactional and time-limited approaches. This study proposes a longitudinal, relationship-based case management framework as an alternative solution. STUDY DESIGN: A nonrandomized, prospective cohort study was conducted among Medicaid enrollees with complex medical and social needs. METHODS: The intervention involved case managers building strong interpersonal relationships over a minimum of 1 year, addressing barriers to care and facilitating solutions. Primary outcomes were total health care expenditures and patient-rated quality of life. RESULTS: The intervention group exhibited a significant reduction in total health care costs over 1 year ( 568 per patient), with greater savings observed for patients with higher preintervention costs. Additionally, an estimated annual savings net of program costs of 48,121 was observed. Patient-rated quality of life showed substantial improvement, evident at both 6 months and 1 year post enrollment. CONCLUSIONS: This study demonstrates the effectiveness of a longitudinal, relationship-based case management approach in improving outcomes for individuals with complex medical, social, and behavioral needs. Unlike transactional interventions, this approach emphasizes partnership and customization, yielding substantial cost reductions and enhanced quality of life. Although limitations exist, including nonrandomization and staff diversity, this study provides a foundation for future research and scalability of similar interventions.