PURPOSE: To analyze the recurrences of atrial fibrillation in patients treated with sotalol or quinidine. METHODS: After conversion to sinus rhythm, 121 patients with paroxysmal atrial fibrillation were randomized to sotalol (58 patients) or quinidine (63 patients) and followed-up during 6 months. Symptoms and ventricular rates on the 12 lead electrocardiogram of the arrhythmic events were compared between the two groups. Clinical and echocardiographic characteristics were analyzed as predictors of atrial fibrillation recurrence. RESULTS: Seventeen (14%) patients relapsed into atrial fibrillation; 7 (12%) were treated with sotalol and 10 (16%) with quinidine. Recurrence occurred later in the sotalol group (median 69 days) in comparison with the quinidine group (median 10 days) (p=0.04). Symptoms were present in 14 (82%) patients during the initial crisis and in 10 (47%) during recurrence. Recurrence was less symptomatic during antiarrhythmic therapy (p<0.04), with no statistical differences between the two groups. Only patients treated with sotalol had ventricular rates during the recurrences lower than during initial crisis (p<0.02). All variables failed to predict recurrence of atrial fibrillation. CONCLUSIONS: evention of atrial fibrillation. Recurrence was less symptomatic during antiarrhythmic therapy. Patients treated with sotalol relapsed to atrial fibrillation later and had ventricular rates during recurrences significantly lower than during the initial crisis.