OBJECTIVE Many patients with type 1 diabetes struggle to self-manage this chronic disease, often because they have a poor knowledge and understanding of the condition. However, little attention has been paid to examining the reasons for this poor knowledge/understanding. To inform future educational interventions, we explored patients’ accounts of the education and information they had received since diagnosis, and the reasons behind gaps in their diabetes knowledge. METHODS Semi-structured interviews were conducted with 30 type 1 diabetes patients enrolled on a structured education programme in the UK. Data were analysed using an inductive, thematic approach. RESULTS Patients’ accounts illustrated a number of knowledge deficits which were influenced by various lifecourse events. Reasons for deficits included: diagnosis at a young age and assumption of decision-making responsibility by parents; lack of engagement with information when feeling well; transitions in care; inconsistency in information provision; and, lack of awareness that knowledge was poor or incomplete. CONCLUSION Patients’ knowledge deficits can arise for different reasons, at different points in the lifecourse, and may change over time. PRACTICE IMPLICATIONS: The delivery of individualised education should take account of the origins of patients’ knowledge gaps and be provided on a regular and on-going basis.