Neonatal hypoglycemia (NH) is one of the most common abnormalities encountered in the newborn. Hypoglycemia continues to be an important cause of morbidity in neonates and children. Prompt diagnosis and management of the underlying hypoglycemia disorder is critical for preventing brain damage and improving outcomes. Congenital hyperinsulinism (CHI) is the most common and severe cause of persistent hypoglycemia in neonates and children, it represents a group of clinically, genetically and morphologically heterogeneous disorders characterised by dysregulation of insulin secretion from pancreatic β-cells. It is extremely important to recognize this condition early and institute appropriate management to prevent significant brain injury leading to complications like epilepsy, cerebral palsy and neurological impairment. Histologically, CHI is divided mainly into two types focal and diffuse disease. The diffuse form is inherited in an autosomal recessive (or dominant) manner whereas the focal form is sporadic in inheritance and is localized to a small region of the pancreas. Recent discoveries of the genetic causes of CHI have improved our understanding of the pathophysiology, but its management is complex and requires the integration of clinical, biochemical, molecular, and imaging findings to establish the appropriate treatment according to the subtype. Here we present a case of sever congenital hyperinsulinism in a girl admitted for lethargy, irritability and general seizures accompanied with profound hypoglycemia, in spite of aggressive medical treatment, she died because of sever congenital hyperinsulinism diazoxide unresponsive.