Catheter ablation of an accessory pathway and atrioventricular node modification using 550 kHz radiofrequency was attempted in 23 children and adolescents between five and 19 years of age (mean = 15.7 years). Fifteen children had accessory-pathway-mediated tachycardia and eight had atrioventricular node reentrant tachycardia. Accessory pathways were present in ten children. Two patients had associated congenital heart disease. Symptoms included disabling palpitations and episodes of syncope. Ablation was attempted from the right and left sides of the heart. Single-catheter technique was used in seven patients. Eleven of the 15 patients with accessory pathways were treated completely. Two patients had recurrences, and one of them died after the arrhythmia surgery. There were two failures. Two patients with incomplete interruption of the accessory pathways were followed up clinically. There were three cases with temporary systemic embolization and one with severe pain related to radiofrequency energy application. Atrioventricular node modification was done by fast-pathway ablation in six, and by slow-pathway ablation in two patients. Two patients with fast-pathway ablation had recurrences of clinical arrhythmia, and one of them underwent a successful second session. There were no complications associated with the procedure in this group of patients. Radiofrequency catheter application was initially successful in 21 (84%) out of 25 procedures, and ultimately curative in 16 (69%) out of 23 patients. There were some serious complications which resolved in the immediate post-procedure period. Radiofrequency catheter ablation appears to be a safe and successful method for the management of supraventricular tachycardia secondary to accessory pathways or atrioventricular node reentrant tachycardia in children and adolescents.