Sudden cardiac death is the most devastating manifestation of hypertrophic cardiomyopathy (HCM) and often occurs in young and previously asymptomatic patients. Therefore, risk stratification for sudden death has a major role in the management of HCM and has acquired even greater relevance since the implantable cardioverter-defibrillator (ICD) has proved to be highly effective in preventing sudden death in this disease. The ICD is definitely indicated for secondary prevention of sudden death in patients with HCM who have survived a cardiac arrest with documented ventricular fibrillation, or experienced one or more episodes of sustained ventricular tachycardia. However, uncertainties persist regarding the precise selection of patients for primary prophylactic ICD implantation. A number of risk markers are used to assess the magnitude of risk, including family history of premature sudden death; extreme left ventricular (LV) hypertrophy (> 30 mm) in young patients; nonsustained ventricular tachycardia on Holter electrocardiographic recording; unexplained (not neurally mediated) syncope, particularly in young patients; and blood pressure decrease or inadequate increase during upright exercise. Multiple risk factors convey a definite increase in risk. However, a single risk factor such as family history of multiple sudden deaths, massive LV hypertrophy in a young patient, or frequent and/or prolonged runs of nonsustained ventricular tachycardia on Holter, may also justify consideration of a prophylactic ICD.