Penetrating atherosclerotic aortic ulcers (PAU) can cause aortic dissection. Of 38 autopsy cases with aortic dissection, 6 (15.8%) had severe atherosclerotic changes, resembling those of PAU, at the site of entry (SE). Clinicopathological data on these patients were compared with those on 32 cases with nonatheromatous dissection (5 with Marfan syndrome or its forme fruste and 27 without Marfan syndrome) and 13 with atherosclerotic saccular aneurysms. For control study, the aorta of a 44-year-old woman who died of pulmonary cancer was used. Compare to nonatheromatous dissection, atherosclerosis-related aortic dissections were found in older women. Four cases were complicated by saccular aneurysms of the aorta. The SE was located in the ascending aorta in 1 and the descending aorta in 5. These sites usually were ulcerated atheromatous plaques or longitudinal fissures rather than transverse tears. Immunohistochemical examination of the SE revealed that MMP-1, 2, 9 and TIMP-2 were expressed in macrophages and/or interstitium, similar to the findings in atheromatous plaque or PAU. We propose that atherosclerosis-related aortic dissection differs from the usual classical aortic dissection. Patients with this lesion have a high risk of re-dissection from the new SE in the same lesion.