The authors report the case of a 32 year old woman with no risk factors for thromboembolism apart from a raised Lipoprotein (a) level, in whom a mobile thrombus of the ascending aorta was diagnosed only by transoesophageal echocardiography after multiple episodes of systemic embolism. After surgical excision the thrombus recurred and death ensued on the 17th postoperative day after multiple visceral embolism despite adequate anticoagulant therapy. This is a rare condition, the outcome of which seems often to be fatal, due to early recurrence irrespective of the treatment (anticoagulant or platelet antiaggregant therapy). This case illustrates the value of systematic transoesophageal echocardiography for the investigation of cerebral or peripheral ischaemic episodes without carotid artery disease and raises the problem of the best way of treating this pathology.