A follow-up study of 49 individuals with paroxysmal atrial tachycardia in infancy is reported. Forty subjects had supraventricular tachycardia and nine had atrial flutter/fibrillation. The mean follow-up period was 24 years. Males whose ECGs showed preexcitation displayed the highest rate of recurrences (approximately 60%) in the long-term follow-up. Approximately 30% of the subjects without preexcitation in the ECG displayed episodes of supraventricular tachycardia in their third decade. Eight-six percent of the children of the subjects in the present series were males. The prognosis is good in the absence of congenital heart disease.