Introduction: Little is known about the real importance of pediatric arrhythmias. Methods: We analyzed the epidemiology, presentation and outcome of all clinically relevant tachyarrhythmias followed up in our pediatric institutions from 1995 to 2006. Results: A total of 250 cases were identified. The mean age ± SD at diagnosis was 4.7 ± 5.3 years, 45 cases were neonatal (18%). Supraventricular arrhythmias were noted in 210 children (84%), ventricular arrhythmias in 40 (16%). The most frequent symptoms were palpitations (n = 71) and syncope (n = 48) in older children, as well as monitoring of diseases (n = 62) and heart failure (n = 49) in younger patients. Recurrence was noted under or after therapy in 75 cases, mostly in cases diagnosed beyond infancy. At long-term follow-up, 169 patients have no recurrence without treatment (of whom 34 had required catheter ablation), 71 are under therapy and 10 died. Conclusion: Supraventricular arrhythmias in younger children are often an incidental diagnosis, respond to antiarrhythmic therapy and have a high incidence of resolution. In older children with supraventricular arrhythmias and in those with ventricular arrhythmias, delayed diagnosis or misdiagnosis is not rare, the arrhythmias are unlikely to resolve spontaneously and long-term antiarrhythmic treatment or catheter ablation is necessary.