The aim of this chapter is to highlight a rare endocrine condition (Congenital Hyperinsulinism, CHI), which can cause low blood glucose levels leading to permanent brain injury. Many Paediatric Nurses are unfamiliar with this condition. CHI is caused by unregulated insulin secretion from the pancreas and typically presents in the newborn period, but it can also present later in life. It is imperative for Paediatric Nurses to be knowledgeable on the subject of CHI as they are usually the first to identify the infant’s low blood glucose levels, often accompanied by non-specific symptoms such as floppiness, jitteriness, fitting, lethargy, or poor feeding. It is always important to consider CHI if an infant or child presents with unexplained recurrent and persistent hypoglycaemia.