Giant cell arteritis may occasionally lead to vessel perforation without previous dissection. At the level of the ascending aorta, however, such an event has been reported only three times. We report a fourth case of impending rupture of the ascending aorta due to a small and isolated lesion of giant cell arteritis. In contrast to previous reports, laboratory and clinical manifestations suggestive of giant cell arteritis were absent in this case so that the diagnosis could only be established on histologic examination of the operative specimen.