The management of pediatric patients with coronary artery fistula (CAF) remains controversial because the clinical course of CAF may vary greatly from spontaneous closure to severe complications. The purpose of our study was to report the outcome of CAF in pediatric patients by using echocardiography as an evaluation tool. Between January 1997 and July 2003, 17 patients (age range, 5 months to 14 years; mean, 3.8 years) with coronary angiographically proven CAF were recruited. We divided patients into two groups. Group 1 (n = 4) included patients with symptoms related to CAF (n = 3), persistent coronary artery dilatation for 6 months (n = 4), and/or a continuous waveform of the fistula detected by Doppler (n = 3). Group 2 (n = 13) included patients who were asymptomatic, with normal coronary artery size or coronary artery dilatation less than 6 months, and/or a noncontinuous waveform of the fistula detected by Doppler. Group 1 patients received interventional therapy, whereas group 2 patients were managed conservatively. There were 6 male and 11 female patients. The correlation coefficient of coronary artery diameter measured on echocardiography and angiography was 0.935 and 0.834 in groups 1 and 2, respectively. The diameter of the involved coronary artery was 5.8-9.2 mm (mean, 7.50 ± 1.85) and 1.7-3.8 mm (mean, 2.72 ± 0.59) in group 1 and group 2, respectively. After transcatheter coil embolization, group 1 patients became asymptomatic with no residual fistula and had decrement of the coronary artery diameter (p = 0.035). All group 2 patients remained asymptomatic with no significant change in coronary artery size (p = 0.846) and 3 of them showed spontaneous closure of CAF. Persistent dilatation of the diameter of proximal coronary artery may be a useful parameter for determining subsequent application of interventional therapy. In patients with nonsignificant CAF, conservative follow-up is strongly suggested and intervention procedures may be unnecessary.