OBJECTIVE Congenital hyperinsulinism (CHI) is a rare condition causing severe hypoglycemia in neonates and infants due to dysregulation of insulin secretion. This study aimed to review 20 years' experience in the management of Taiwanese children with CHI. METHODS Between 1990 and 2010, children diagnosed with CHI and followed up at the Pediatric Endocrine Clinic of the National Taiwan University Hospital were enrolled. Their medical records were thoroughly reviewed. RESULTS In total, 13 patients (8 boys and 5 girls) were enrolled, including six patients with onset of hypoglycemia within 1 month of age and seven patients at 4.0 ± 2.1 months of age. The birth weight standard deviation scores of these two age groups were 4.6 ± 1.8 and 1.4 ± 1.3 standard deviation score, respectively (p < 0.01). Initial intravenous glucose infusion at rates of 22.9 ± 5.3 mg/kg/min and 13.4 ± 5.6 mg/kg/min, respectively, were mandatory to maintain euglycemia in these two groups (p < 0.05). All received pancreatectomy after failure of initial medical treatment. Twelve patients were followed up for a period of 2.5-19.8 years. Eight of them remained euglycemic without any medication and three patients developed diabetes mellitus. Seven of the nine patients who underwent intelligence evaluation had normal mental outcomes. Mental retardation of two patients was too severe to be evaluated. All four patients with mental retardation had a delay in the maintenance of euglycemia, and three of them also had seizure disorder. CONCLUSIONS The age at onset of hypoglycemia reflects the severity of CHI. Early diagnosis and appropriate treatment are important for favorable mental outcomes.