Congenital hyperinsulinism (CHI) is one of the most common causes of persistent hypoglycemia during infancy. There are two morphological forms: diffuse and focal. Early recognition of CHI is vital in preventing neuroglycopaenic brain injury. An appropriate therapy can protect against long-term sequelae, such as diabetes mellitus. We present the case of a 13-year-old girl who was diagnosed with congenital hyperinsulinism during first weeks of life. Initially, medical management with somatostatin analogues (octreotide) was attempted. Because medical therapy failed, subtotal pancreatectomy was performed. During the 13-year observation following this treatment, no hypoglycemia recurrence or carbohydrate metabolism disorders were observed. Patient’s current problems are  overweight and hypercholesterolemia, as well as a recently diagnosed autoimmune thyroid disease. The paper presents characteristic aspects, diagnostic difficulties, and the consequences of congenital hyperinsulinism.