Patients with hypertrophic cardiomyopathy (HCM) frequently have arrhythmias and hemodynamic abnormalities, and are prone to sudden death and syncope. There is an important need for improved identification of patients at risk for sudden death and definition of appropriate investigation and therapy. The relation of 31 clinical, Holter, cardiac catheterization and electrophysiologic (EP) variables to subsequent cardiac events in 230 patients at high risk for sudden death was examined using multivariate analysis. Risk evaluation was for cardiac arrest in 32, syncope in 80, presyncope in 52, ventricular tachycardia (VT) on Holter in 36, a strong family history of sudden death in 9, and palpitations in 21 patients. Sustained VT was induced in 82 (36%) patients. Seventeen cardiac events (8 sudden deaths, 1 cardiac arrest and 8 syncope with defibrillator discharges) occurred during a follow-up 28 + 19 months. The 1-year and 5-year event-free rates were 99% and 79%, respectively. Two variables were significant independent predictors of subsequent cardiac events: inducibility of sustained ventricular arrhythmia, and a history of cardiac arrest/syncope. Only two sudden deaths occurred in 66 patients without symptoms of impaired consciousness: one sudden death occurred in 36 patients with non-sustained VT on Holter and one sudden death occurred in 30 patients without VT on Holter. Notably, none of 51 patients without symptoms of impaired consciousness or inducible VT had a cardiac event. Thus, in HCM 1) VT on Holter is of benign prognostic significance in the absence of symptoms of impaired consciousness and inducible VT, and 2) inducibility of sustained VT at EP study specially when associated with cardiac arrest or syncope identifies a subgroup of patients at high risk for subsequent cardiac events.