The congenital long QT syndrome (LQTS) is a familial disorder characterized by a prolongation of the QT interval on the ECG and occurrence of life-threatening cardiac arrhythmias especially, but not only, under conditions of increased sympathetic activity. Symptomatic untreated patients are at high risk for sudden cardiac death. Twelve LQTS genes have been identified and most of them encode cardiac ion channels. Very effective therapies are available and in carefully treated patients mortality is around 0.5–1% over 20years. The initial treatment should always involve β-blockers, with propranolol and nadolol being the two most effective ones. With few exceptions all mutation carriers should be treated because of the risk of sudden death during the first cardiac event. Approximately 20% of patients continue to have syncope despite the β-blockers and the most rationale next level of therapy is represented by Left Cardiac Sympathetic Denervation (LCSD), which is highly effective and can complement any other therapy. One important limitation of LCSD is that, without valid reasons, it is available only in a few selected centers. Whenever syncope recurs despite LCSD, or whenever an aborted cardiac arrest has occurred, it becomes logical to resort to the implantation of a cardioverter defibrillator (ICD). The latter, however, is burdened by a high rate (31%) of adverse events including severe ones such as endocarditis, inappropriate shocks, and by the need of frequent battery replacements. A scoring system, based on simple clinical variables, can identify the patients more and less likely to benefit from ICD implantation.