Hypertrophic cardiomyopathy (HCM) is an inheritable condition that may cause sudden death in the absence of significant symptoms or adverse morphological features. Therefore, there is a need for identification of those patients at sufficiently high risk to warrant prophylactic treatment. Risk stratification for primary prevention of sudden death has relied upon non-invasively derived markers of risk: syncope; a family history of premature sudden death; nonsustained ventricular tachycardia on Holter; abnormal blood pressure response to exercise; and severe left ventricular hypertrophy. The presence of two or more risk factors is associated with a 6-year sudden death survival rate of 72% (56-88%), justifying the consideration of prophylactic therapy. The 6-year sudden death survival rate in patients with one or no risk factors is 94% (91-98%). In these individuals the context and severity of the risk factor may guide the decision for prophylaxis; for example, a highly malignant family history carries greater justification than a large pedigree with only one sudden death. There is a need, however, for determining risk more accurately in those individuals with only one conventional risk factor. Programmed stimulation has been studied for its predictive value in primary prevention. 'Aggressive' protocols have been used and the most commonly induced arrhythmia is polymorphic ventricular tachycardia. These findings, however, are non-specific and of limited prognostic value. In addition the patients studied have been from selected high-risk populations without a low-risk cohort for comparison. Thus invasive EP studies appear to carry little advantage over non-invasive risk stratification. This is not surprising given that the mechanisms of cardiac arrest in HCM can be varied and may be modified by abnormal vascular responses and ischaemia. The relevance of invasively induced arrhythmias may therefore be limited. Other uses for electrophysiological study include the investigation and treatment of individuals with conduction disease and/or Wolff-Parkinson-White syndrome, atrial flutter and fibrillation and monomorphic ventricular tachycardia. Appropriate management may then involve radiofrequency ablation. A permanent pacemaker will be required if the atrio-ventricular node is ablated.