Background— We investigated the role of phenotypic characteristics in stratifying the risk of sustained ventricular arrhythmias in patients harboring arrhythmogenic right ventricular dysplasia/cardiomyopathy–associated mutations. Methods and Results— Clinical, electrocardiographic, and arrhythmic outcome (composite measure of first occurrence of sustained ventricular tachycardia/resuscitated sudden cardiac death/sudden cardiac death/appropriate implantable cardioverter-defibrillator therapy) data were obtained for 215 patients (104 families; 85% PKP-2). During a mean follow-up of 7 years, 86 (40%) patients experienced the arrhythmic outcome. Event-free survival was significantly lower among probands ( P <0.001) and symptomatic ( P <0.001) patients. Integration of ECG repolarization and depolarization abnormalities allowed for differential risk categorization. Event-free survival at 5 years for the low-risk ECG group (0–1 T inversions or minor depolarization changes) was 97% versus 81% for the intermediate-risk ECG group (2 T inversions+minor depolarization changes) versus 33% for the high-risk ECG group (≥3 T inversions±major or minor depolarization changes; P <0.001). Incremental arrhythmic risk was seen in patients with increasing premature ventricular complex count on a Holter ( P <0.001). Proband status (hazard ratio, 7.7; 95% confidence interval, 2.8–22.5; P <0.001), ≥3 T-wave inversions (hazard ratio, 4.2; 95% confidence interval, 1.2–14.5; P =0.035), and male sex (hazard ratio, 1.8; 95% confidence interval, 1.2–2.8; P =0.004) were independent predictors of the first arrhythmic event on multivariable analysis. Conclusions— Pedigree evaluation, an ECG, and a Holter examination provide for comprehensive arrhythmic risk stratification in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy–associated mutations. We propose an approach to risk stratification based on these variables.