Glycogen storage disease type I (GSD I) is characterized by impaired production of glucose from glycogenolysis and gluconeogenesis resulting in severe fasting hypoglycaemia. The aim of the present study was to examine the efficacy of a continuous subcutaneous glucose monitoring system (CGMS MiniMed), to determine the magnitude and significance of hypoglycaemia in GSD I and to evaluate the efficacy of its dietary treatment. Four children with GSD I were studied over a 72-h period. Results indicated that the values recorded with continuous subcutaneous glucose monitoring were highly correlated with paired blood glucose values measured by glucometer. Significant periods of asymptomatic hypoglycaemia were noted, especially during night-time. The study suggests that repeated continuous subcutaneous glucose monitoring may serve as a useful tool for the assessment of the long-term management of GSD I patients.