For many young people and their parents, nocturnal hypoglycaemia is perhaps the most feared short-term complication of diabetes. Intensive diabetes control is beneficial for all people with the condition – maintaining good blood glucose control overnight is critical in reducing the body’s exposure to high glucose levels. But it increases the risk of a dangerous drop in blood glucose levels while people are asleep. David Dunger and Roman Hovorka describe the problem of nocturnal hypoglycaemia and look forward to future developments that might reduce and eventually eradicate the risks.