In the management of hypertrophic cardiomyopathy the goals should be the control of symptoms, and the identification and treatment of those at high risk. Arrhythmias, particularly atrial fibrillation and nonsustained ventricular tachycardia, are common in adult patients with hypertrophic cardiomyopathy. Atrial fibrillation has long been thought to herald an ominous prognosis, but this is probably not the case, and in the majority of patients atrial fibrillation can be controlled without accelerated symptomatic deterioration. Uncontrolled observations indicate that low-dose amiodarone may be the most useful drug in both paroxysmal and chronic atrial fibrillation. The detection of nonsustained ventricular tachycardia on ambulatory ECG monitoring remains the single most useful indicator of the risk of sudden death in the adult patient, and the treatment of choice is again low-dose amiodarone. The mechanism of sudden death, and the mode of action of amiodarone in preventing it, are not known for certain in the majority of patients. The risk of sudden death is higher in children and adolescents, but arrhythmias are less common, and no useful predictive marker of increased risk has been found. The roles of invasive electrophysiological studies and the implantable cardioverter-defibrillator are still being evaluated.