Atherosclerosis is one of the major causes of morbidity and mortality in patients with type 2 diabetes mellitus. Pioglitazone has been reported to have antiatherogenic effects. The aim of this study was to investigate whether pioglitazone affects pulsatility index (PI) of the cerebral arteries and the carotid intima-media thickness in type 2 diabetic patients. A total of 40 type 2 diabetic patients were included in this study. They were divided into 2 groups: the pioglitazone-treated group (pioglitazone 15 mg/d with gliclazide 80-320 mg/d for 12 weeks) and the gliclazide-treated group (gliclazide 80-320 mg/d for 12 weeks). Transcranial Doppler ultrasonography was performed for each cerebral artery, and PI was calculated as (systolic velocity-diastolic velocity)/mean velocity. The pioglitazone treatment significantly increased high-density lipoprotein cholesterol and decreased triglyceride levels and insulin resistance. This study revealed that the change in mean intima-media thickness was not significant in both groups, but the change in PI was significantly decreased with pioglitazone compared to gliclazide. In conclusion, pioglitazone decreased PI and improved cerebrovascular resistance in type 2 diabetic patients.