Atrial fibrillation (AF) is associated with an increased risk of stroke. In patients with chronic AF, without clinically known cerebrovascular disease, computed tomography (CT) has revealed a high frequency of abnormal low-density areas suggesting old asymptomatic infarcts. To investigate the frequency of such lesions in paroxysmal AF, 30 patients with paroxysmal AF and 30 controls matched in sinus rhythm, without history of cerebrovascular disease, were CT scanned. Four patients with paroxysmal AF (13%) and 3 controls (10%) had abnormal CT scans with areas of low density with sharp demarcation from surrounding tissue. The abnormal areas probably reflected small, clinically silent infarcts. There were no differences between paroxysmal AF and controls in number and size of abnormal areas with apparent tissue loss. In contrast to chronic AF, the risk of such lesions in paroxysmal AF does not seem to be increased compared with matched sinus rhythm controls. This is in agreement with the clinical experience of a low risk of stroke in paroxysmal AF.