In childhood, GSD type III causes relatively severe fasting intolerance, classically associated with ketotic hypoglycaemia. During follow up, history of (documented) hypoglycaemia, clinical parameters (growth, liver size, motor development, neuromuscular parameters), laboratory parameters (glucose, lactate, ALAT, cholesterol, triglycerides, creatine kinase and ketones) and cardiac parameters all need to be integrated in order to titrate dietary management, for which age-dependent requirements need to be taken into account. Evidence from case studies and small cohort studies in both children and adults with GSD III demonstrate that prevention of hypoglycaemia and maintenance of euglycemia is not sufficient to prevent complications. Moreover, over-treatment with carbohydrates may even be harmful. The ageing cohort of GSD III patients, including the non-traditional clinical presentations in adulthood, raises new questions.