BACKGROUND It is clear that permanent cardiac pacing in patients with sick sinus syndrome is effective. In spite of a normal pacemaker function, syncope may occur. Causes often remain unknown. The objective of this study was to review our current experience with these patients to identify predictors and etiologies of these symptoms. RESULTS We studied 153 patients who received atrial, ventricular and dual-chamber pacemakers for sick sinus syndrome. During a median follow-up of 57.6 months (1-177 months), actuarial incidence of syncope or near syncope was 4.5% at 1 year, 9% at 5 years and 13% at 10 years. Causes were related with autonomic insufficiency (45%), pacemaker/lead malfunction (30%), pacemaker syndrome (10%) and conduction disturbances in patients with AAI pacemakers (10%). In only one patient (5%) syncope remained unexplained. Preimplant predictors for syncope were gender (male) and age (< 70 years old). CONCLUSIONS 1) Syncopes in paced patients with sick sinus syndrome have multiple etiologies and may be multifactorial; 2) Autonomic dysfunction and "oversensing" in troubleshooting of implanted cardiac pacemakers could provide an explanation for recurrent syndrome in over 70% of these patients; 3) A better evaluation of neurogenic syncope may be necessary before pacemakers are implanted, to prevent recurrent syncope.