The cases of two young patients with repetitive syncopal attacks due to idiopathic long QT syndrome (ILQTS) are reported. Both had been primarily misdiagnosed for seizures. In one of the cases the QT interval in the ECG at rest was normal. The same patient had a previous episode of cardiac arrest with ventricular fibrillation. The treadmill stress test was of great value, revealing polymorphic ventricular tachycardia induced by exercise, and evaluating the efficacy of beta-blocking therapy in the follow-up. The ILQTS should be considered a possible etiology in any patient presenting with new onset seizures, especially in the young. The treatments were different in both cases. In the first one, the treatment with nadolol (100 mg od) revealed to be very effective with total remission of symptoms. The treadmill stress test performed 15 days after the beginning of treatment did not show any ventricular arrhythmias, and it was assumed that the patient was effectively protected against ventricular arrhythmias. After 4.5 months of follow up, no syncopal episodes occurred. In the second case due to young age, the frequency, and the severity of the attacks (cardiac arrest with ventricular fibrillation), and the inefficacy of beta-adrenergic-blocking agents, the implantable cardioversor-defibrillator was the treatment chosen, although the beta blocking therapy was maintained to reduce the number of arrhythmic events. The ILQTS is a rare anomaly related to sudden cardiac death. The ILQTS is characterised by the association of several distinctive electrocardiographic features, among which prolongation of the QT interval is the best known. Life-threatening arrhythmia occurs usually under conditions of physical or psychological stress. Relatively effective therapies do exist and are represented by antiadrenergic interventions: beta-adrenergic-blocking agents are the treatment of choice. When they fail, left sympathetic denervation or the automatic implantable cardioversor-defibrillator have also proved to be effective.