Echocardiographic measurement of left atrial size was performed in 24 patients (13 males, 11 females, median age 56 years) with idiopathic paroxysmal atrial fibrillation (IPAF). A second measurement was done, after a mean period of 20 months. Our study showed that: (1) the patients with IPAF had normal-sized atria, the dimensions of which remained unmodified over a 20-month period; and (2) no correlation was found between the frequency of recurrent arrhythmic episodes and left atrial size. Since atrial enlargement, which is the known risk factor for embolic stroke, was not observed in our patients, we conclude that patients with IPAF do not need anticoagulant therapy.