Two models were validated in this longitudinal study including one which predicted sudden death and one which predicted diagnostic arrhythmias on monitoring. The model for prediction of sudden death was developed in patients in whom a cause of syncope was not established by initial history and physical examination. The predictors in this model included a history of diabetes mellitus, renal insufficiency, left ventricular hypertrophy, left bundle branch block, and left axis deviation. The model of predictors of diagnostic arrhythmias was developed in patients in whom a cause of syncope was not established from initial history, physical examination, or EKG and included a history of ventricular tachycardia and an abnormal EKG by specific criteria.