To investigate mid- to long-term outcomes in children with coronary artery fistula (CAF). Methods: We retrospectively reviewed the medical records of patients seen between September 1996 and August 2011. We enrolled those diagnosed with CAF via echocardiography (Philips SONOS 7500 system and Philips IE33) or angiography. The mean follow time was 42.58 ± 3.4 months (range, 1–166 months). For comparative purposes, participants were grouped as acquired versus congenital, and symptomatic versus asymptomatic. We also measured the size of the coronary artery (CA) in patients with CA dilatation (CAD). Results: Out of 122 CAF patients, spontaneous closure was detected in 37 patients at 21.59 ± 3.45 months after diagnosis. This timeframe did not differ between the acquired and congenital groups (21.64 ± 6.26 months vs. 21.57 ± 4.15 months; p = 0.991). Ninety patients were asymptomatic and remained so; their spontaneous closure rate was 28.89%. Moreover, 24 patients had CAD, including 17 with Kawasaki disease and seven with congenital CAF. The CAs of all congenital-CAF-plus-CAD patients were initially > 5 mm; these patients underwent percutaneous transcatheter intervention, and their CA sizes decreased significantly (6.11 ± 0.79 mm vs. 3.76 ± 0.36 mm; p = 0.002). Conclusion: With the advanced sensitivity of echocardiography, CAF can be detected more easily than ever before. Most patients with small CAFs are asymptomatic and may experience spontaneous closure. Therefore, management of CAF depends on symptoms; if patients are asymptomatic and have small CAFs, intervention may not be necessary, especially in acquired cases. However, if patients present with symptoms or persistent dilatation of the proximal CA, surgical or percutaneous closure should be performed.