OBJECTIVE To investigate the prevalence of underlying, inducible supraventricular arrhythmias in patients referred for ablation of atrial fibrillation (AF). RESULTS Electrophysiology study reports of 409 consecutive patients (18% female), aged 55 +/- 9 years, who were referred for catheter ablation of AF, were studied. At electrophysiology study, arrhythmias other than AF were induced in 31 patients (7.6%). Cavotricuspid-dependent atrial flutter was induced in 15 patients (3.7%), slow-fast atrioventricular nodal re-entrant tachycardia (AVNRT) in seven patients (1.7%), atrioventricular re-entrant tachycardia (AVRT) due to an accessory pathway in five patients (1.2%), and atrial tachycardia (AT) in four patients (0.98%). Specific ablation aimed at elimination of the underlying arrhythmia only was performed in 13 patients, isolation of the pulmonary veins without additional ablation in three patients, and a combined procedure was performed in the remaining 15 patients. No significant association was observed between type of induced arrhythmia and type of ablation performed (P = 0.338). Slow pathway ablation without pulmonary vein isolation was more common among patients with AVNRT (five patients, 71%). AF recurrence was higher among patients in whom atrial flutter was induced at electrophysiology study (eight patients, 53%) compared to those with AVRT (no patient), AT (no patient), or AVNRT (one patient) (P = 0.03). CONCLUSIONS Patients referred for ablation of paroxysmal AF should be investigated for evidence of underlying supraventricular arrhytmias. In patients with AVNRT, slow pathway ablation may be the only procedure that is necessary for cure of AF. Inducibility of atrial flutter appears to carry an increased risk of AF recurrence regardless of whether the cavotricuspid isthmus is also ablated.