Anomalous origin of either the left main coronary artery (LMCA) or right coronary artery (RCA) from the aorta with subsequent coursing between the aorta and pulmonary trunk is a rare and sometimes fatal coronary artery anomaly. Thirty-two cases of these anomalies were reviewed, with particular attention to the exact location and shape of the anomalistically positioned ostium and coronary dominance. The LMCA (7 cases) arose either from behind the right coronary sinus (6 cases) or as a single ostium with the RCA straddling the right-left commissure and right coronary sinus (1 case). In 5 of the 7 cases, the anomaly was fatal. In 6 cases of anomalous origin of the LMCA, the RCA was dominant and in 4 the anomaly was fatal. In only 1 case of anomalous origin of the LMCA was the left circumflex coronary artery dominant, and in this case the anomaly also was fatal. The RCA (25 cases) arose either from behind the left coronary sinus (8 cases), above the left coronary sinus (5 cases), from above the right-left commissure (10 cases) or as a single ostium with the LMCA above the right-left commissure and left coronary sinus (2 cases). In 8 of these 25 cases the anomaly was fatal. In 7 cases of anomalous origin of the RCA, the left circumflex coronary artery was dominant and in no case was the anomaly clinically significant. In 1 case, both the RCA and left circumflex coronary artery were hypoplastic and the anomaly was fatal. Coronary dominance, not ostial shape, was useful in separating the clinically significant from the clinically insignificant anomalies.