Purpose: to assess specificities of course of the long­QT syndrome in children before and after implantation of cardioverter­defibrillator (ICD), and optimization of indications to ICD­therapy.Materials and methods. We included in this study 48 children with long­QT syndrome from 44 unrelated families (28 boys and 20 girls), who underwent ICD implantation at the mean age 11.8±3.8 years. Mean duration of follow­up after implantation was 5.2±2.8 years. Data from these children were compared with those from 59 children of comparable age and gender with long­QT syndrome from 46 unrelated families receiving antiarrhythmic therapy (β­adrenoblockers). We assessed clinical and electrocardiographic characteristics of the disease obtained at initial visit and their dynamics thereafter.Results. Children with long­QT syndrome and ICD were mainly probands with interval QT longer than 500 ms, recurrent syncope and often history of sudden cardiac arrest requiring high doses of β­adrenoblockers for control of ventricular tachyarrhythmias.Conclusion. ICD implantation is an effective and safe method both of primary and secondary prevention of sudden cardiac death in children with long­QT syndrome.