Floating thrombus in the ascending aorta is rare and its association with papillary thyroid adenocarcinoma has not been documented. We report a case of a 64-year-old man who was referred to our emergency unit because of suspected type A aortic dissection. Computerized tomographic and transthoracic echocardiographic scans revealed a floating thrombus in the aneurysmatic ascending aorta. The thrombus was removed with the dilated aorta. Although the aortic wall was macroscopically normal, histologic examination revealed metastatic papillary adenocarcinoma.