Of the different kinds of coronary anomalies observed in adults, anomalous origin of a coronary artery from the opposite sinus of Valsalva with an "interarterial" course (ACAOS) entails a high risk of clinical consequences related to the intramural course of the ectopic coronary artery. We review current imaging modalities for differentiating this condition from generally benign coronary anomalies and for quantifying the severity of individual cases. For identifying ACAOS, noninvasive modalities (echocardiography, computed tomographic angiography, and coronary magnetic resonance angiography) are preferred: the favored modalities are transthoracic echocardiography in children and multidetector computed tomography in adults. For evaluating the pathophysiologic mechanisms of ischemia in ACAOS and subclassifying the severity of individual forms, coronary intravascular ultrasonography provides enhanced temporal and spatial resolution. The critical quantifiable features of the coronary anatomy in ACAOS seem to be hypoplasia, lateral compression at the level of the intramural course, and possibly exercise-related further narrowing of the proximal ectopic segment. Definitive guidelines are being developed for the optimal workup and treatment of ACAOS.