BACKGROUND/AIMS@#The aromatase inhibitors (AIs) are well known anti-hormonal therapy in endocrine-responsive breast cancer patients. It can lead to dyslipidemia and be the risk factor of cardiovascular disease due to low estrogen level. However, some recent studies comparing AIs with placebo have shown controversial results. The aim of this study was to investigate lipid profiles, measurement of carotid intima-media thickness (IMT) and the presence of plaque among endocrine-responsive breast cancer treated with AIs compared to ones that were not treated with AIs.@*METHODS@#A total of 85 postmenopausal women, who underwent breast cancer surgery during the age of 50 to 64 without history of statin use were included. There were 42 patients who were treated with AIs over 1 year (group 1) and 43 patients without AIs use (group 2). Serum total cholesterol, high density lipoprotein cholesterol, triglycerides, fasting blood glucose, carotid IMT, and presence of plaque were assessed.@*RESULTS@#The baseline characteristics were similar between two groups and there was no significant difference in carotid IMT irrespective of AIs administration. However, ultrasonographic evaluation of carotid artery revealed that the presence of plaque in AI users was significantly higher than in non-AI users (66.7% vs. 41.9%, p = 0.02; odds ratio, 4.21 in adjusted model; p = 0.01). History of diabetes was also the significant risk factor for the plaque formation.@*CONCLUSIONS@#There was no significant difference in lipid profile itself between two groups, but more importantly the presence of the plaque was much higher indicating possible detrimental effect of AI on cardiovascular system.