The purpose of this retrospective study was to investigate the clinical characteristics in pediatric patients with supraventricular or ventricular tachycardia. Sixty-nine pediatric patients were included. Age distribution at first episode of tachyarrythmia, most indicative symptoms and signs, associated conditions and long-term prognosis were determined for the different mechanisms of tachyarrythmia. 78% of the children had supraventricular tachycardia and 22% ventricular tachycardia. At diagnosis, 57% of the children with supraventricular tachycardia were younger than 1 year. The majority of infants were detected during routine investigation without having any complaints whereas the majority of children presented with symptoms. Recurrence was rare in cases diagnosed during infancy, but was usual in cases diagnosed beyond infancy.