Congenital hyperinsulinism (CHI) is a common cause of hypoglycemia in infants. We report three cases of CHI with differing clinical, biochemical, and molecular genetic spectra. One patient was unresponsive to medical treatment and died after subtotal pancreatectomy because of complications due to the surgery. Two patients have been followed successfully with medical treatment. Early diagnosis and appropriate treatment of CHI are essential to prevent morbidity and mortality.