The epidemiology of paroxysmal atrial fibrillation (PAF) is poorly known because of the difficulties in setting up trials to study this condition. Its biannual incidence is about 2 per thousand. Its prevalence is 1 to 2% in a population of over 65 years of age. Paroxysmal atrial fibrillation is often asymptomatic. An initial episode of atrial fibrillation may remain a single event in a number of cases. Isolated paroxysmal atrial fibrillation progresses to permanent atrial fibrillation in about 20% of cases, usually if there is underlying cardiac disease. Rheumatic valve disease, cardiac failure, hypertension, previous myocardial infarction and cerebrovascular accidents are often associated with paroxysmal atrial fibrillation. Embolic complications are rare if paroxysmal atrial fibrillation is isolated.