Patients with myotonic dystrophy are reported to have a higher frequency of sudden death than the general population. Although causes of sudden death in myotonic dystrophy are suggested to be due to conduction of defects progressing, the HV interval cannot predict whether conduction system disease would develop or progress. We report two cases of myotonic dystrophy complicated with sustained monomorphic ventricular tachycardias (VT), which can cause sudden death. In Case No. 1, although the patient was treated successfully for sustained VT with verapamil in electrophysiologic studies, another sustained VT was confirmed 2 years later. In Case No. 2, the patient showed decreased left ventricular ejection fraction and late potentials, and induced sustained VT that was identical to clinically documented VT. Although VT is believed to be rare in patients with myotonic dystrophy, these cases suggest that VT is a possible cause of sudden death.