Expression of functionally active thrombomodulin (TM) on endothelial cells is critical for vascular thromboresistance. 3-Hydroxyl-3-methyl coenzyme A reductase inhibitors (statins) can protect the vasculature from inflammation and atherosclerosis caused by cholesterol-dependent and cholesterolindependent mechanisms. In the present study, the effects of atorvastatin on TM expression in the aorta of cholesterol-fed rabbits and in TNFa-treated human aortic endothelial cells (HAECs) were investigated. When rabbits were fed a 0.5% cholesterol diet with and without supplementation with atorvastatin for 9 weeks, the neointimal area in the thoracic aorta of the atorvastatin-treated group was significantly reduced and there was significant induction of TM protein expression. In HAECs, TNFa treatment decreased the expression of TM in a time- and dose-dependent manner and atorvastatin pretreatment upregulated the expression of TM mRNA and protein in HAECs with or without TNFa treatment. Atorvastatin also inhibited monocyte adhesion to control and TNFa-treated HAECs via TM expression. ERK1/2 phosphorylation was significantly reduced by 24 h pretreatment with atorvastatin, whereas TNFa increased the phosphorylation of the MAPKs, p38, JNK, and ERK1/2. Blocking the transcriptional activation of NF-kB and nuclear translocation of NF-kB p65 prevented the TNFa-induced downregulation of TM. Atorvastatin regulated TM expression in control and TNFa-treated HAECs by inhibiting the activation of ERK and NF-kB. The increase in endothelial TM activity in response to atorvastatin constitutes an important pleiotropic effect of this commonly used compound and may be of clinical significance in cardiovascular disorders in which deficient endothelial TM plays a pathophysiological role.