Hyperinsulinism is the most common cause of hypoglycemia in infants. In many cases conservative treatment is not effective and surgical intervention is required. Differentiation between diffuse and focal forms and localization of focal lesions are the most important issues in preoperative management. We present a case of persistent infancy hyperinsulinism. Clinical presentation, conservative treatment modalities, diagnostic possibilities of focal and diffuse forms, and surgical treatment, which led to total recovery, are discussed.