Congenital coronary artery fistula (CAF) is an infrequent vascular anomaly that establishes a direct link between an epicardial coronary artery and a cardiac chamber, major vessels, or other vascular structures. In this case there was an aneurysmal-CAF between a left main trunk and the right atrium, which was initially diagnosed as a Kawasaki disease by transthoracic echocardiography and subsequently confirmed by coronary angiography and multi-slice CT angiography. A multi-slice CT angiography might well become the modality of choice for the characterization of these rare congenital anomalies.