Thiazolidinediones (TZD), which are widely used as insulin sensitizers, and fibrates, which are lipid-lowering drugs, are used in the treatment of dyslipidemia that commonly accompanies diabetes. Several reports suggest elevated levels of high-density lipoprotein (HDL) cholesterol, but the paradoxical reduction of HDL cholesterol level during single or combined TZD and fibrate therapies has been occasionally reported. Herein, we report a case of paradoxical decrease in HDL cholesterol and apolipoprotein A-1 levels during rosiglitazone and fenofibrate treatment for the first time in Korea. The patient was a 56-yr-old man presenting with type 2 diabetes mellitus and dyslipidemia. His HDL cholesterol and apolipoprotein A-1 levels returned to normal after the cessation of fenofibrate therapy. Since diabetes is an established risk factor of cardiovascular diseases, low HDL cholesterol can be a key cause of concern for patients with diabetes. Therefore, HDL cholesterol level should be determined before and after starting TZD and/or fibrate therapy in diabetic patients.