Background Patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) carry the risk of ventricular arrhythmias and sudden cardiac death (SCD). This study investigated the prognostic information of modified moving average T-wave alternans (MMA TWA) in patients with ARVD/C. Methods A total of 63 consecutive patients (mean age, 44.7 ± 14.8 years; 38 men) with ARVD/C were enrolled. Baseline characteristics and structural and electrocardiographic parameters were obtained. All patients underwent ambulatory electrocardiographic examination at the time of diagnosis, and MMA TWA data were exported for further analysis. Events were defined as documented SCD or ventricular tachyarrhythmias during clinical follow-up. Results During a mean follow-up of 28.1 ± 15.4 months, 19 of 63 (30.2%) patients experienced events, including SCD in 2 patients (10.5%) and ventricular tachyarrhythmias in 17 patients (89.5%). Patients with events had higher TWA within modified V5 and V1 channels than did those without events (54.7 ± 24.9 μV vs 35.0 ± 18.3 μV; P = 0.004; 58.8 ± 27.6 μV vs 38.4 ± 18.6 μV; P = 0.007, respectively). After multivariate Cox regression analysis, maximal TWA derived from either the modified CM5 or NASA channel predicted the occurrence of events (P < 0.001; hazard ratio, 1.06; 95% confidence interval, 1.03-1.10). At the cutoff value of > 66 μV, maximal TWA yielded a sensitivity and a specificity of 89.5% and 90.5%, respectively, in predicting SCD or ventricular tachyarrhythmias. Conclusions The initial analysis of MMA TWA could provide prognostic implications in the prediction of SCD or ventricular tachyarrhythmias in patients with ARVD/C.