Background: In spite of successful pulmonary vein (PV) isolation and substrate modification, success rates of catheter ablation of atrial fibrillation (AF) have not yet reached the levels of other supraventricular tachycardias. In this context, the identification and elimination of non-PV foci has been considered the important issue to improve success rates. Methods: In a series of 233 consecutive patients with paroxysmal AF (PAF, n=157) and persistent AF (PeAF, n=76), endocardial mapping of atrial ectopic beats initiated AF was performed before and after PV isolation. Using a multielectrode catheter, we localized the earliest activation during the spontaneous or induced ectopic beats initiating AF. In cases of sustained AF, internal cardioversion was performed and spontaneous reinitiation of AF (IRAF) was observed. Radiofrequency energy was delivered to eliminate these foci at the site of earliest activation. Results: Fifty six (24.1%) patients had a total of 63 non-PV foci (18.7% in PAF, 35.1% in PeAF). In PAF, non-PV foci included the interatrial septum (34.5%, 10), superior vena cava (31.0%, 9), crista terminalis (17.2%, 5), coronary sinus ostium (13.8%, 4), left atrial posterior wall (3.4%, 1), and ligament of Marshall (3.4%, 1). In PeAF, non-PV foci included the interatrial septum (70.4%, 19), crista terminalis (14.8%, 4), superior vena cava (11.1%, 3), coronary sinus ostium (7.4%, 2), and left atrial appendage (3.7%, 1). Four (7.1%) of patients with non-PV foci were difficult to map precisely because of sporadic unpredictable discharge and repeated induction of sustained AF (3.4% in PAF, 11.1% in PeAF). During a mean follow up of 8.7 짹 6.9 months, there was no correlation between non-PV foci and the recurrence of AF (28.6% in patients with non-PV foci vs. 23.7% in patients without non-PV foci, P=NS). However, patients with non-PV foci originating from interatrial septum had a higher recurrence rate compared to those originated from SVC (34.5% vs. 8.3%, P<0.05, respectively). Conclusions: Identification and effective elimination of non-PV foci, especially interatrial septum and SVC origin, may be helpful to maximize the curative efficacy for PeAF as well as PAF.