Atherosclerotic disease of the thoracic aorta is common in the elderly and patients with clinical coronary artery disease. Although embolization can occur from atherosclerotic debris within the thoracic aorta, it is not commonly considered in the differential diagnosis of the source of a systemic embolism. In the current study, the prevalence, clinical significance and embolic potential of intraaortic atherosclerotic debris as detected by transesophageal echocardiography was determined. Intraaortic atherosclerotic debris was identified in 38 (7%) of 556 patients undergoing transesophageal echocardiography. An embolic event occurred among 11 (31%) of the 36 study patients with intraaortic atherosclerotic debris. The incidence of an embolic event was higher when the debris was pedunculated and highly mobile (8 [73%] of 11 patients) than when it was layered and immobile (3 [12%] of 25 patients) (p less than 0.002). Among 15 patients undergoing an invasive procedure of the aorta, the incidence of embolism was 27%. In conclusion, in a patient with an embolic event, the thoracic aorta should be considered as a potential source. Transesophageal echocardiography can reliably detect intraaortic atherosclerotic debris, and when it is identified, an invasive aortic procedure should be avoided if possible.