Fructose-1,6-bisphosphatase deficiency is a disorder of gluconeogenesis. Most of the time patients are healthy and do not require a special diet. Infections, fasting or vomiting can lead to serious illness, with drowsiness, tachypnoea, marked acidosis and hypoglycaemia. However, hypoglycaemia occurs at a relatively late stage. Treatment aims to prevent metabolic decompensation by giving glucose by mouth or intravenously. In young children, bicarbonate is often needed to correct acidosis.