Background: The purpose of this study was to determine the timing of ventricular arrhythmias requiring implantable cardioverter-defibrillator (ICD) therapy in patients with early repolarization syndrome (ERS) versus Brugada syndrome (BS).. Methods: We analyzed data from 32 patients who underwent ICD implantation for ERS or BS at Asan Medical Center. Appropriate shocks for ventricular arrhythmias were analyzed in one-hour time interval. ERS was defined as J point elevation (��� 0.1 mV) in two consecutive in inferior or lateral leads. Results: Twenty patient with BS (18 men, 49짹15 years) and 12 patients (10 men, 46짹9 years) with ERS were included. During follow-up period (7.6짹2.4 years in BS, 8.6짹3.0 years in ERS, p=0.3), the number of patients who experienced appropriate shocks were higher in ERS (4 of 20 in BS vs. 7 of 12 in ERS, p=0.03). The total number of shocks was 348 (including 274 shocks in one patient). The timing of ventricular arrhythmia showed uneven, nocturnal distribution (see figure) both in BS and ERS patients. Conclusions: Marked diurnal variation with a night-time peak was observed in patients with ERS as well as BS.