The purpose of this study was to review the initial experience of a university hospital with Implantable Loop Recorders (ILR) for diagnosis of recurrent unexplained syncope or presyncope. Twelve patients with syncope or presyncope of unknown etiology (who had a negative tilt table test, electrophysiologic study, and neurologic work-up) underwent implantation of ILR. All implants were performed using the Reveal ILR (Medtronic AVE, Santa Rosa, California). The 8 cc device is 61 mm long, 19 mm wide, 8 mm thick and weighs 17 grams. It has 18 months of battery life and has 2 electrodes with 38.5 mm spacing. The device is nonvascular and is implanted approximately 2 fingerbreadths below the clavicle in a subcutaneous pocket (1.5 inches long) and is secured via polydacron suture to the pre-pectoral fascia/pectoralis muscle. Twelve patients with a mean age of 61 +/- 22 years received the ILR. Ten patients had syncope and 2 had presyncope. Three patients had coronary artery disease and 2 had dilated cardiomyopathy. ILRs were implanted for a mean follow-up period of 7.2 +/- 5.8 months (range, 1 day to 18 months). Two patients still continue to be monitored at the time of this report. The mean number of events prior to ILR was 6.0 +/- 5.4. Eight patients (66%) had recurrent syncope after implantation. One patient was not available for follow-up. There were no significant complications from the implant. In 5/12 patients (42%), the ILR helped to diagnose the etiology of the syncopal episode. Syncope was secondary to asystole in three patients, junctional bradycardia in another patient, and seizure activity in a fifth patient (high-frequency noise recorded on the electrocardiogram during sinus rhythm). The 4 patients with ILR-documented bradyarrhythmias underwent permanent pacemaker implantation and are alive and well. ILR implantation is a simple, useful and safe method in assisting with the diagnosis of recurrent unexplained syncope or presyncope after an inconclusive electrophysiologic and neurologic evaluation.