Epidemiological data indicate that estrogens significantly reduce the risk of morbidity and mortality due to cardiovascular diseases in postmenopausal women. Although numerous animal studies demonstrated inhibition of early atheromatous lesion formation by estrogen treatment in several species, information about the potential benefits of estrogens on complex, advanced atherosclerotic lesions is still lacking. The present study was designed to test whether chronic treatment with 17 beta-estradiol affects hyperglycemia-induced premature advanced lesion formation in 40-week-old male apolipoprotein E-deficient (Apo E-KO) mice. In order to accelerate advanced lesion formation, we treated male Apo E-KO mice with streptozotocin (STZ) at the age of 6 weeks. Two weeks later the STZ-treated mice received a slow release pellet containing either 17 beta-estradiol or placebo. STZ treatment caused sustained hyperglycemia without changes in serum total cholesterol or triglyceride levels compared to citrate control mice. STZ-treated Apo E-KO mice developed significantly more lesions in some (but not all) parts of the aorta and its main branches, and caused premature calcified cartilaginous metaplasia in the lesions of the proximal aorta. Chronic treatment with 17 beta-estradiol lead to a significant decrease in blood glucose and triglyceride levels, reduced the lesion area in all vascular segments studied and prevented cartilaginous metaplasia in STZ-treated Apo E-KO mice. The results of this study show that STZ treatment leads to significant acceleration of atherosclerotic lesion formation and premature occurrence of calcified cartilaginous areas in Apo E-KO mice, which could be effectively prevented by chronic estrogen treatment.