Purpose: Atrial flutter is an uncommon arrhythmia in the neonatal period. This study aimed to describe the cause and clinical course of atrial flutter in neonates.Methods: The medical records of 14 patients diagnosed with atrial flutter at Ulsan University Hospital Neonatal Intensive Care Unit (NICU) between March 2008 and August 2020 were reviewed retrospectively.Results: All 14 cases occurred on the first day of birth. Of these, two were term infants, and 12 were preterm infants. Causes of atrial flutter included three cases of the umbilical venous catheter misplacement, one with a diabetic mother, and one ivolving atrial flutter after an intravenous aminophylline injection. Thirteen patients had structurally normal hearts with no congenital heart diseases. The patient, born to a diabetic mother, had an atrial septal defect and ventricular hypertrophy. Adenosine was administered first to differentiate it from paroxysmal supraventricular tachycardia. Synchronized cardioversion was attempted in 11 patients, while one received it after an esmolol injection that failed to convert to sinus rhythm. One patient had a recurrence after the intrusion of a peripherally inserted central catheter; however, atrial flutter disappeared after repositioning it. No patient had a recurrence after discharge.Conclusion: Neonatal atrial flutter is a rare tachyarrhythmia with the risk factors often unknown; however, it could occur in structural heart disease, mispositioning of the umbilical venous catheter, and if the mother has diabetes. During umbilical venous catheterization, clinicians should be cautious and ensure appropriate monitoring of infants in the NICU as it may cause complications.