Background <p>Equitable access to healthcare is critical for effective diabetes management; however, evidence on the role of regional-level spatial accessibility in diabetes management remains limited. This study examined the associations of regional spatial accessibility to primary care, together with having a usual source of care, with diabetes management outcomes.</p> Methods <p>We conducted a nationwide longitudinal study utilizingthe Korean National Health Insurance Database (NHID), which included 81,588 patients newly diagnosed with type 2 diabetes in 2014. Patients were followed from 2015 to 2019, with annual observations of those using diabetes care services.Outcome measures included medication adherence, regular outpatient visits, and recommended monitoring tests. Key explanatory variables comprised regional-level spatial accessibility to primary care facilities and the presence of a usual source of care (USC). Analyses employed generalized estimating equations.</p> Results <p>Regional-level spatial accessibility exhibited a positive gradient for hemoglobin A1c and lipid panel testing, with patients in the highest accessibility areas being 12% and 3% more likely, respectively, to receive these tests than those in the lowest accessibility areas. In contrast, having a USC was consistently associated with improved medication adherence (adjusted relative risk [aRR]: 1.16, 95% confidence interval [CI]: 1.15–1.16) and more regular outpatient visits (aRR: 1.39, 95% CI: 1.38–1.40), highlighting the importance of USC for routine management. However, USC was not positively associated with complication-monitoring tests. These findings indicate that while USC facilitates routine care, access to regional healthcare infrastructure is more crucial for diagnostic testing uptake.</p> Conclusions <p>This study demonstrates that regional-level spatial accessibility and individual-level healthcare utilization characteristics are associated with diabetes management in different ways. While having a USC was strongly correlated with enhanced medication adherence and regular visits, regional disparities in healthcare resources were linked to disparities in diagnostic test uptake. These findings provide evidence to inform policies aimed at strengthening continuity of care and reducing disparities in spatial accessibility in chronic disease management.</p>