To assess the risk-benefit of electrophysiologic studies (EPS) in very elderly patients, we studied 104 consecutive patients 80 years or older who underwent EPS during hospitalization. Seventy-two percent of the patients had a history of coronary artery disease, and 7% had an acute myocardial infarction during the hospitalization. Other cardiac disorders included valvular heart disease (17%) and cardiomyopathy (12%). Abnormal systolic left ventricular function was common, with a left ventricular ejection fraction of 30% or less in 25% of the patients. The most common indication for EPS was unexplained syncope or presyncope (62 patients). Other indications for EPS included evaluation of cardiac arrest (9 patients), sustained monomorphic ventricular tachycardia (7), nonsustained ventricular tachycardia (22), wide QRS tachycardia (1), symptomatic sinus bradycardia (2) and palpitations (1). Thirty-eight patients (37%) demonstrated EPS findings considered to be responsible for the patients' symptoms. Specific clinical characteristics of the patients were not predictive of abnormal EPS findings. After EPS, 60% of the patients had a change in therapy; more than 75% of the patients who presented with sustained ventricular tachycardia or who had survived cardiac arrest and 58% of patients who presented with syncope had a change in therapy after EPS. Complications secondary to EPS occurred in only 3 patients; mortality or neurological complications were not associated with the procedure. We conclude that EPS can be performed safely in very elderly patients and that the procedure is beneficial in that therapy is modified on the basis of the EPS findings.