Hypoglycaemia is a major side-effect of insulin treatment. It is known that young children with type 1 diabetes mellitus (T1DM) show a higher risk of hypoglycaemia than older children. This study was performed to analyse the incidence of hypoglycaemia within the first 14 days (day 1-day 14) of insulin treatment in children at the onset of T1DM and to evaluate the influence of age and insulin dosage. The Paediatric Quality Initiative (DPV), including data from 121 centres in Germany and Austria, provided anonymous data of 1,680 patients (age 0.7-18.8 years; 799 girls) at the onset of T1DM. Hypoglycaemia was defined as a blood glucose level (BG) < 2.8 mmol/l (50 mg/dl). The hypoglycaemia rate rose continuously from day 2 (4.8% ) to day 5 (11.2% ) and then remained stable between 8.7% -11.2% until day 14. The hypoglycaemia rate was higher in younger than in older children ( P < 0.0001). Multiple regression analysis revealed an influence of age ( P < 0.0001), insulin dosage ( P =0.0034), and route of initial treatment ( P =0.0052) on the hypoglycaemia rate. From day 2 to day 14, the insulin dosage itself was higher in females than in males ( P =0.0147), in patients with high HbA1c ( P =0.0001), high BG ( P < 0.0001), or low pH ( P < 0.0001). There was no influence of age on the insulin dosage. Conclusion: During the first 14 days after onset of type 1 diabetes mellitus, young children, intravenous-treated patients and patients receiving a high insulin dosage are at particular risk of developing hypoglycaemia. In order to avoid hypoglycaemia, blood glucose should be measured frequently and the insulin dosage should be carefully adjusted. Low blood glucose levels should be treated promptly. This is was the incidence of hypoglycaemia within the first 14 days (day 1-day 14) of insulin treatment in children at the onset of T1DM and to evaluate the influence of age and insulin dosage. The Pediatric Quality Initiative (DPV), including data from 121 centres in Germany and Austria, provided anonymous data of 1,680 patients (age 0.7-18.8 years; 799 girls) at the onset of T1DM. Hypoglycaemia was defined as a blood glucose level (BG) <2.8 mmol / l (50 mg / dl) The hypoglycaemia rate rose continuously from day 2 4.8%) to day 5 (11.2%) and then remained stable between 8.7% -11.2% until day 14. The hypoglycaemia rate was higher in younger than in older children (P <0.0001). Multiple regression analysis revealed an influence of age ( P <0.0001), insulin dosage (P = 0.0034), a From day 2 to day 14, the insulin dosage itself was higher in females than in males (P = 0.0147), in patients with high HbA1c (P = 0.0001), High-BG (P <0.0001), or low pH (P <0.0001). There was no influence of age on the insulin dosage. Conclusion: During the first 14 days after onset of type 1 diabetes mellitus, young children, intravenous-treated patients and patients receiving a high insulin dosage are at particular risk of developing hypoglycaemia. In order to avoid hypoglycaemia, blood glucose should be measured frequently and the insulin dosage should be carefully adjusted. Low blood glucose levels should be treated promptly.