Background and Objectives竊�The aim of this study was to investigate the safety and effectiveness of radiofrequency catheter ablation (RFCA) for supraventricular tachycardia (SVT) in young children and the characteristics of the tachycardia which need RFCA. Subjects and Methods竊�From March 2000 to August 2011, 95 (55 males, 40 females) of 335 RFCA procedures were performed at an age less than 10 years. According to the age, the patients were divided to two groups (Group 1; 0-4 years old, n=24, Group 2; 5-9 years old, n=71). Results竊�Total 89 patients got RFCA for SVT, 6 patients had RFCA twice due to recurrence of arrhythmia. Eleven patients had associated congenital heart anomaly. Nine patients had arrhythmia- associated ventricular dysfunction and 7 had fetal tachycardia. Fetal tachycardia was more frequent in Group 1 (25% vs 1.4%, p<0.001). Wolff-Parkinson-White syndrome (44.2%) and unidirectional retrograde accessory pathway (35.8%) were popular reasons of arrhythmia. Among 76 patients with atrioventricular reentrant tachycardia, 16 (21%) had multiple accessory pathways (AP). Atrioventricular nodal reentrant tachycardia (AVNRT, 10.5%) and ectopic atrial tachycardia (EAT, 8.4%) were frequent. RFCA for AVNRT was done exclusively in Group 2. Half of patients with EAT had tachycardia induced cardiomyopathy. Median onset of tachycardia was 1.1 (0.02-4.1) years after birth in group 1 and 5.7 (0.05-9.6) years in group 2 (p<0.001). The main reasons of RFCA were poorly controlled arrhythmia (21.1%) and symptomatic tachycardia (34.7%). However, drug resistant arrhythmia was more frequent in group 1 (33.3% vs 4.2% p<0.001). RFCA was initially successful in 97.9% without major complication. Tachycardia recurrence rate was 11.6%. Recurrence was more common in multiple AP patients than single AP patients (33.3% vs. 12.1% respectively, p=0.048). Multiple AP was more common in the patients with AP located at right atrioventricular groove. Ultimately only two patients have mild symptom of tachycardia after subsequent procedures. There was no significant difference in success rate, recurrence rate, procedure time and fluoroscopy time between two age groups. Conclusion竊�RFCA is effective and safe treatment for supraventricular tachycardia in young children.