A 22-year-old woman with type Ia glycogen storage disease was referred to the endocrinology department with new-onset diabetes mellitus-glycated haemoglobin (HbA1c) of 8.2% . She had suffered from repeated bouts of hypoglycaemia since the first days of her life . The diagnosis was made at 5 months old, after clinical investigations revealed mixed dyslipidaemia, lactic acidosis and hepatomegaly . Compound heterozygosity was documented at the age of 4 . The basis of her initial treatment was starch and reinforced soy milk, ingested multiple times a day and night . The patient suffered from obesity since childhood . This case shows a rare association between glycogen storage disease type Ia and diabetes mellitus . A multidisciplinary approach was implemented . Through diet and use of flash continuous glucose monitoring, we were able to improve patient's adherence and metabolic profile . Hypoglycaemia and hyperglycaemia risk significantly decreased; 86% time in range (70-180 mg/dL), 6% hypoglycaemia and 6.3% HbA1c in recent evaluations.