Patients with hypertrophic cardiomyopathy are at increased risk for sudden 
death. Recent studies have improved our ability to risk-stratify such patients 
and have elucidated several potential mechanisms of sudden death and syncope. 
Certain noninvasive tests, such as signal-averaged electrocardiography and 
measurements of cardiac autonomic function and QT/QT dispersion, are often 
abnormal in hypertrophic cardiomyopathy, but are not useful for risk 
stratification. Myocardial ischemia determined by exercise thallium 
scintigraphy, however, identifies young patients with hypertrophic 
cardiomyopathy who are at high risk for cardiac arrest and syncope. Nonsustained 
ventricular tachycardia on ambulatory Holter monitoring in the absence of 
symptoms of impaired consciousness is associated with a benign prognosis and is 
not predictive of sudden death. Conversely, ventricular tachycardia induced at 
electrophysiologic study identifies adult patients with hypertrophic 
cardiomyopathy who subsequently experience sudden death. Finally, 
characterization of the natural history of the genetic defects will increasingly 
become an integral part of risk evaluation in hypertrophic cardiomyopathy.