Early repolarization syndrome (ERS) has traditionally been regarded as benign. In the electrocardiogram (ECG), it is characterized by a diffuse upward ST-segment concavity ending in a positive T wave in leads V2-V4 (5). Clinical interest in this ECG phenomenon has recently been rekindled because of similarities with the electrocardiographic manifestations of the highly arrhythmogenic Brugada syndrome and the potential for misdiagnosis. This article addresses the clinical characteristics and cellular and ionic basis for ERS. In experimental models, the ECG signature of ERS can be converted to that of the Brugada syndrome, raising the possibility that ERS may not be as benign as generally thought, and that under certain conditions known to predispose to ST-segment elevation, patients with ERS may be at greater risk. Further clinical and experimental data are clearly required to test these hypotheses, and the characteristics of ERS need to be more fully delineated within the framework of what has been learned about the Brugada syndrome in recent years.