We report a case of rapidly fatal aortic dissection which was unusual because no intimal tear was present and no blood was present in the dissected aortic wall, although the dissection involved the entire aorta. Death was considered to be due to acute myocardial ischaemia from dissection involving the left coronary artery. Prominent cystic medial necrosis was present. There was no history of hypertension and only histological evidence of left ventricular hypertrophy. No other clinical or pathologic states associated with aortic dissection were present. Although cystic medionecrosis was the probable cause in this case, it is present in only a small proportion of patients in the absence of Marfan's syndrome, and more recently investigated defects in the composition of aortic wall connective tissue components may be more relevant factors in the causation of many cases of aortic dissection.