Recurrence of atrial fibrillation (AF) after electrical cardioversion of chronic AF is not uncommon. However, it remains unclear which parameter(s) predict clinical recurrence. To assess the potential predictors of clinical recurrence after successful electrical cardioversion, we analyzed clinical, echocardiographic and electrophysiologic parameters in 36 patients (age 63 ± 11 years; 26 males, 10 females) with chronic persistent AF lasting more than 3 months. The dimensions of the left atrium and left ventricular end diastole and end systole were measured by echocardiography. The P wave characteristics from the surface 12-lead electrocardiogram (ECG) were studied in sinus rhythm. Atrial local activations were studied by biatrial basket electrode mapping in AF. With a mean of 7 ± 2 months of follow-up, 17 (47%) patients had AF recurrence despite multiple antiarrhythmic drug therapy. None of the clinical or echocardiographic parameters were relevant to the recurrence. However, among the surface ECG and intraatrial electrophysiological parameters, the mean P wave duration was the only independent predictor of the risk of clinical recurrence after successful electrical cardioversion. The sensitivity and predictive accuracy of recurrence were 82 and 70%, respectively, when the mean P wave duration was more than 125 ms.