It is conventionally thought that electrical cardioversion in patients with atrial fibrillation (AF) of longstanding duration or with a large left atrial diameter, only seldom results in long term success. Recurrence is common, although antiarrhythmic drugs often effectively decrease the number and duration of recurrent AF episodes. We analysed clinical, functional and pharmacological variables which could possibly influence the long term outcome after a first electrical cardioversion for AF in a retrospective study on 85 patients. Univariate and multivariate analysis was used to identify factors predicting maintenance of sinus rhythm at 100 days, and absence of recurrence during the entire follow-up. In univariate analysis, the only significant predictor for maintenance of sinus rhythm at 100 days was the duration of the preceding AF episode. Multivariate analysis with persistence of sinus rhythm at 100 days as endpoint confirmed this as a prognostic factor (p < 0.03), but sotalol treatment also contributed to maintenance of sinus rhythm (p < 0.05). When considering the entire observation period, class III antiarrhythmic drugs, i.e. sotalol and amiodarone, were useful in preventing recurrence (p < 0.01 and < 0.02). High age (above 75 years) was a predictor of recurrence. In conclusion, class III antiarrhythmic drugs, the duration of atrial fibrillation and high age were the most important determinants of long term outcome, while echocardiographic parameters and the presence of heart disease played no role.