The J-wave has been reported to be associated with life-threatening ventricular arrhythmia. However, the clinical implication of the J-wave is still unclear in patients with an implantable cardioverter defibrillator (ICD).The study population consisted of 170 ICD patients (age, 56 ± 16 years, 79.4% male) treated at Kitasato University Hospital between 2003 and 2014. Ventricular fibrillation (VF) and ventricular tachycardia (VT) events were documented via ICD interrogation, and the patients were divided into 3 groups: 1) VF event group, 2) VT event group, and 3) No-event group. To predict VT or VF events, univariate and multivariate analysis of clinical data including ECG findings were performed. A J-wave was defined as the presence of notching or slurring of the QRS complex (≥ 0.1 mV) in inferior/lateral leads. Among the 170 patients examined, 23 experienced VF and 38 experienced VT during 54 ± 39 months follow-up. In the multivariate Cox proportional hazards model, the J-wave was identified as an independent predictor for a VF event (HR: 3.886, 95% CI: 1.313-10.568, P = 0.012). In contrast, BNP (HR: 1.002, 95% CI: 1.000-1.003, P = 0.043) and left ventricular diastolic diameter (HR: 1.039, 95% CI: 1.002-1.081, P = 0.049) were independent predictors for a VT event.The results suggest J-waves in the stable phase in an ECG may be a useful predictor for a VF event in ICD patients.