We report the results of radiofrequency catheter ablation in 203 patients under 18 years of age with supraventricular tachyarrhythmias between April 1992 and June 1997. The presence of an accessory pathway caused the tachyarrhythmia in 181 patients (89.1%) with a total of 187 accessory pathways; atrioventricular nodal reentry caused the arrhythmia in 18 patients (8.8%) and atrial flutter in only 4 patients (1.9%). We eliminated the accessory pathway in 171 patients (91.4%), 23 patients showed recurrence of the tachycardia and we had complications in 4 patients (2.1%). The procedure was successful in the treatment of the atrioventricular nodal reentry in the 18 cases, with ablation of the slow pathway in 17 cases and in only one patient of the fast pathway, one patient showed total A-V block, and recurrence of the arrhythmia in 3 cases (16.6%). Finally the procedure was successful in the 4 cases of atrial flutter with one recurrence (25%). In the total of the series, the radiofrequency catheter ablation was successful in 193 patients (95%), with recurrence of the arrhythmia in 27 cases (13.3%) and with complications in only 5 patients (2.6%). Radiofrequency catheter ablation is a safe and effective procedure for the definitive treatment of supraventricular tachyarrhythmias in children.