A case of a male 34-year-old Type 1 diabetic patient who experienced a prolonged severe hypoglycaemic episode is presented. After the hypoglycaemic event, the patient suffered from moderate to severe neuropsychological impairments. On the basis of neuropsychological assessment results, diabetes therapy was modified (less complex insulin regimen, fixed insulin doses and fixed carbohydrate distribution). At a follow-up examination (3 months), presumable complete recovery of cognitive function was observed. This case demonstrates the possible detrimental neuropsychological effects of severe hypoglycaemia, that, in this case, turned out to be reversible. It highlights the clinical implications of impaired cognitive function on self-care and self-management abilities and the usefulness of neuropsychological testing in clinical diabetes care.