The penetrating atherosclerotic ulcer of the aorta resulting from the atherosclerosis of the aortic wall can clinically mimic type III aortic dissection, since both diseases produce the ulceration and dissection of aortic wall. However, their imaging features and pathophsiologies are distinctly different from each other. Familial hypercholesterolemia(FH) menifests overt hyperlipidemia that can results in premature atherosclerosis of the aorta as well as the coronary artery. We report a clinically and radiologically evident case of perntrating atherosclerotic ulcer of the descending thoracic aorta which was developed in a 36-year-oldd heterozygote FH male.