Hyperinsulinism is a rare disorder, affecting one in more than 50,000 births. It was initially thought to be due to a diffuse anomaly called nesidioblastosis, but interventional radiology-based studies demonstrated the existence of two separate forms, one difuse and the other focal. These invasive techniques have now been replaced by PET studies with 18F fluorodopa. Focal forms can be cured by surgical removal of the lesion, while the diffuse form can be treated medically or by subtotal resection of the pancreas. Biochemical and genetic studies show that focal and diffuse forms are due to various mutations of chromosome 11.