The idiopathic long QT syndrome (LQTS) carries a high mortality in untreated patients. Administration of beta-receptor antagonists is considered the treatment of choice. Data concerning the usefulness of implantable cardioverter-defibrillator (ICD) therapy in this condition are sparse. We report on a 29-year-old female with LQTS who was treated with propranolol, but also underwent implantation of an ICD as a fail-safe therapy. During the next 17 months, the patient was asymptomatic. However, after skipping her propranolol for 3 days, she had several syncopal spells with concomitant device therapy. ICD interrogation revealed a total of 55 nonsustained runs of ventricular tachycardia and 16 sustain ed episodes that were correctly identified by the device and respectively terminated by the first shock. This case report demonstrates that in selected patients with the LQTS, using ICD therapy as a fail-safe treatment may be life-saving, particularly when compliance to medical therapy is uncertain.