Atherosclerosis is a disease which affects large and medium-sized arteries. Typical features of atherosclerosis are accumulation of intra- and extracellular lipids, foam cell formation, proliferation of smooth muscle cells and accumulation of connective tissue. Plasma lipids and lipoproteins play an important role in the formation of atherosclerotic lesions. Recent evidence suggests that oxidation of low-density lipoprotein (LDL) may play an important role in the pathogenesis of atherosclerosis. Incidence of cardiovascular disease increase significantly after menopause. Part of the increase is due to atherogenic changes in plasma lipoproteins, i.e. increase in LDL and decrease in high density lipoprotein (HDL). Clinical endpoints of cardiovascular diseases are usually caused by atherosclerosis and thrombosis, both of which can be influenced after menopause by sex steroids. Hormone replacement therapy has anti-atherogenic effects on plasma lipoprotein fractions. Recent evidence also suggests that estrogens may have several protective effects on the vascular wall, including direct inhibition of LDL degradation, oxidation and smooth muscle cell proliferation.