OBJECTIVES: To investigate immediate and follow-up treatment results of transcatheter closure of patent ductus arteriosus (PDA) in infants less than 5kg. METHODS: Between January 2005 and December 2009, 227 patients underwent transcatheter closure of PDA in Severance Cardiovascular Center. Among them 23 patients were less than 5kg. We retrospectively reviewed the clinical outcomes of these patients. RESULTS: Of the total 23 patients, 22 patients underwent successful transcatheter closure of PDA. The PFM Nit-Occlud (PFM AG, Cologne, Germany) was used in 5 cases, COOK Detachable Coil (COOK Medical Inc, Bloominton, IN, USA) was used in 1 case, and Amplatzer Duct Occluder (AGA Medical Corp., Plymouth, MN, USA) was used in 17 cases. Median body weight was 4.5kg (3.2-5kg) and median age was 3months (1-8months). The mean PDA size and the mean device size were 3.6짹1.4mm and 4.6짹1.3mm, respectively. The mean Qp/Qs ratio was 2.8짹1.2. The mean procedure time and fluoroscopic running time were 52.8짹28.1 minutes and 12.0짹5.9 minutes. No major complications were observed in all the patients. No significant pulmonary artery nor aortic stenosis was observed after the procedure. No significant residual shunt flow remained in all patients at last follow-up. CONCLUSIONS: Transcatheter closure of PDA in carefully selected infants less than 5kg is a safe and effective treatment.