Background: Adiponectin is an adipocyte-derived plasma protein with various anti-atherogenic properties. However, the effect of statins on insulin sensitivity and plasma level of adiponectin remainscontroversial. Methods: Forty-eight non-diabetic, hypercholesterolemic patients were enrolled and assigned to statin treatment (atorvastatin 10 or 40 mg) group (n=27) or no statin treatment group (n=21). In addition, another 20 age-and sex-matched non-diabetic, normocholesterolemic patients were enrolled as control group. Insulin sensitivity (indicated by HOMA index) and plasma level of adiponectin were determined before and 6 weeks after treatment in all patients. Results: The HOMA index (1.76±0.81 vs. 1.42±0.57, p=0.09) and adiponectin level (8.22±2.83 μg/dl vs. 9.23±4.36 μg/dl, p=0.26) were similar between hypercholesterolemic and normocholesterolemic patients. The treatment with statin did not affect the fasting plasma level of glucose, insulin or HOMA index, suggesting the neutral effects of statins on insulin sensitivity. However, the treatment with statin significantly reduced the plasma level of adiponectin (from 8.6±3.1μg/ml to 7.8±3.2μg/ml, P=0.01). All of these variables did not change in the no statin treatment group. Conclusion: The result of this study showed that the insulin sensitivity and the plasma level of adiponectin were similar between hypercholesterolemic and normocholesterolemic non-diabetic patients. Although treatment with statins for 6 weeks did not deteriorate insulin sensitivities, the plasma level of adiponectin significantly decreased