Background and aims: impaired awareness of hypoglycaemia (IAH) is an important predictor for severe hypoglycaemia, particularly in type 1 diabetes. IAH and its effects are largely unknown outside Europe and North America. The global Hypoglycaemia Assessment Tool study aimed to assess hypoglycaemia incidence and awareness in patients with T1D and type 2 diabetes in Northern Europe, Canada, Eastern Europe, the Middle East, Latin America, South East Asia and Russia. Materials and methods: Hypoglycaemia awareness was assessed at baseline using a validated method based on the question: ‘Do you have symptoms when you have a low sugar level?’. The answer ‘always’ implied normal awareness, ‘usually’ impaired awareness, ‘occasionally’ and ‘never’ unawareness. Severe hypoglycaemia was reported in 6-month retrospective and 1-month prospective periods. Results: in T1D 45% declared normal awareness, 39% impaired awareness and 17% unawareness. People with unawareness had the highest estimated annual incidence ratesfor severe hypoglycaemia both retrospectively and prospectively. Patients with unawareness were older (47.6 years), had longer diabetes duration (21.3 years), and lower HbA1c (62.3 mmol/mol) than those with awareness. Regionally, in T1D, the association between severe hypoglycaemia and IAH was most pronounced in Eastern Europe (retrospective IRs: always 1.36; usually 1.71; occasionally 2.18; never 3.08), but an inverse association was uniquely observed in SE Asia (retrospective IRs: always 2.90; usually 1.92; occasionally 0.91; never 0.27). In T2D, 45% reported normal awareness, 30% impaired awareness and 25% unawareness. Slightly lower IRs for severe hypoglycaemia were observed with reduced awareness particularly in the retrospective period. In contrast to T1D, patients with unawareness were younger (60.6 years) with a shorter duration of diabetes (12.9 years) and insulin use (5.2 years) and had higher HbA1c (65.1 mmol/mol) than those with awareness. Conclusion: the HAT study shows the expected prevalence of hypoglycaemia unawareness and its association with increased risk of severe hypoglycaemia in T1D in some but not all parts of the world. In T2D, an unexpected higher prevalence of unawareness was found and an inverse association with severe hypoglycaemia.