Recent data from the Centers for Disease Control and Prevention show that sudden cardiac death accounts for approximately 400,000 deaths annually in this country. The survival rate for these patients is dismal. Because of the low probability of survival from a cardiac arrest, there has been an increasing focus on primary prevention. The implantable cardioverter defibrillator (ICD) is a highly effective treatment to abort potentially fatal arrhythmic episodes. Thus, various trials have been conducted to determine methods to best identify patients at high risk for sudden arrhythmic death. This review focuses on the epidemiology of sudden cardiac death and risk stratification approaches that have been tested to determine whether they can identify populations likely to benefit from an ICD.