Without the concept of primary prevention of sudden cardiac death, therapy with implantable defibrillators would not have reached the current distribution and clinical importance. Most of the scientific evidence of the concept is based on clinical studies from 1996-2005. More than 75 % of all defibrillator implantations are currently indicated as primary prevention. Implantable converter-defibrillator (ICD) therapy in the primary prevention of sudden cardiac death was incorporated into scientific guidelines starting in 1998. The historical development of the indications for ICD therapy in the primary prevention of sudden cardiac death is presented, reflecting major results of controlled, randomized clinical studies and guideline discussions.