Anomalous origin the left coronary artery from the pulmonary artery (ALCAPA) is an extremely rare congenital coronary abnormality that may be difficult to diagnose by echocardiography. Most patients present with a potentially fatal illness leading to sudden cardiac death during infancy. This report describes a 15-year-old girl who had 15-year history of cardiac murmur but with no clinical symptoms. Echocardiographic examination was normal, but a 320-slice computed tomographic (CT) scan showed the anomalous origin of the left coronary artery form the pulmonary artery. This case demonstrates that the 320-slice CT scan is a sensitive and reliable technique for establishing the diagnosis of ALCAPA in both symptomatic and asymptomatic patients when it cannot be visualized by echocardiography.