Four hundred sixty-two patients, all with either documented spontaneous sustained ventricular tachycardia or cardiac arrest unresponsive to other antiarrhythmic drugs (2.6/patient), were treated with amiodarone. Thirty-five patients (7.6%) failed to respond or died during the initial oral or intravenous loading phase. The remaining 427 patients were discharged on treatment with oral amiodarone and followed up for up to 98 months. Recurrence of ventricular tachycardia or sudden cardiac death at 1, 3 and 5 years by life-table analysis was 19%, 33% and 43%, respectively, for patients discharged on amiodarone therapy. The sudden cardiac death rate was 9%, 15% and 21%, respectively, at 1, 3 and 5 years. Side effects were reported by 45% of patients after 1 year, by 61% after 2 years and by 86% after 5 years. Amiodarone was discontinued because of side effects in 14%, 26% and 37% of patients after 1, 3 and 5 years, respectively. Incidence rates of recurrence of arrhythmia, sudden cardiac death and side effects were highest in the early months and then decreased. By multivariate analysis, advanced age, low ejection fraction and a history of cardiac arrest were independent risk factors for sudden cardiac death during amiodarone therapy.