Hyperglycaemia and glucose variability occur frequently during critical illness or after major surgery in children and are associated with worse outcome. Association does not necessarily imply causality however, and the question whether tight glycaemic control (TGC) with insulin infusion improves morbidity and mortality can only be answered by randomised controlled trials (RCTs). Currently, only one single-centre RCT exists, proving the concept of TGC in critically ill children. Attenuation of inflammation and reduction of secondary infections, decreased prolonged stay in intensive care and reduced dependency on haemodynamic support were accomplished, despite a substantial increased incidence of biochemical hypoglycaemia. Before universal implementation in paediatric intensive care both long-term effects on outcome and development and issues regarding optimal levels of blood glucose control need to be cleared in multicentre prospective RCTs. Technological improvement might be helpful in optimising blood glucose control.