Although radiofrequency catheter ablation has been used extensively to treat refractory supraventricular tachycardia in adults, few data are available on its safety and efficacy in children and adolescents. We reviewed registry data obtained from 24 centers to evaluate the indications, early results, complications, and short-term follow-up data in young patients who underwent this procedure. Standardized data were submitted for 652 patients who underwent 725 procedures between January 1, 1991, and September 1, 1992. The mean length of follow-up was 13.5 months. The median age of the patients was 13.5 years, and 84 percent of them had structurally normal hearts. The initial success rates for ablation of atrioventricular accessory pathways (508 of 615 procedures) and atrioventricular-node reentry (63 of 76 procedures) were both 83 percent. Greater institutional experience in performing ablation in children and location of the accessory pathway in the left free wall correlated with greater likelihood of sustained success. Conversely, a right free-wall pathway, the presence of other heart disease, and higher body weight were all associated with a lesser chance of sustained success. Recurrences of arrhythmia accounted for 45 percent of the failures overall in the series. Atrial ectopic-focus tachycardia had the highest recurrence rate. The total complication rate was 4.8 percent (35 of 725 procedures), and the only variables that independently correlated with a higher complication rate were very low weight and less institutional experience. These early results suggest that radiofrequency catheter ablation has a good success rate and a low complication rate in pediatric patients, especially when it is carried out in experienced pediatric cardiology centers.