Purpose: The purpose of this study was to explore the association between glycaemic levels and health literacy in outpatients with Type 1 (T1D) and Type 2 diabetes (T2D). Methods: A cross-sectional study at Steno Diabetes Center Aarhus, Denmark, included 3,070 outpatients with T1D and T2D, of which 1,252 responded (403 T1D, 849 T2D). HbA1c values were analysed in tertiles, and health literacy was assessed using the Health Literacy Questionnaire (HLQ™) across four dimensions: (1) managing health and critical assessment, (2) appraisal of health information, (3) active engagement with healthcare providers, and (4) understanding health information for self-management. Linear regression models assessed the association between HbA1c tertiles and health literacy for both diabetes types. health information. Results: T1D outpatients in tertile 3 (mean HbA1c = 71.5 mmol/mol, range = 62–148), had lower education, higher comorbidity, poorer well-being, and increased anxiety, depression, and diabetes-related stress compared to tertile 1 (mean HbA1c = 47.4 mmol/mol, range = 29–53). High HbA1c was linked to lower health literacy in three of four dimensions. In T2D patients, high HbA1c was associated with longer diabetes duration, poorer well-being, higher stress and anxiety, and difficulties in understanding Conclusion: This study finds that outpatients with poor glycaemic control have lower health literacy than those who have tighter glycaemic control. It also highlights the important fact that many diabetes patients struggle to understand health information, regardless of their HbA1c levels. Further research is needed to refine strategies that help healthcare providers support effective diabetes management