PURPOSE: Carotid duplex scan is a frequent option for initial carotid artery evaluation. There has been debates about accuracy of peak systolic velocity (PSV) >125 cm/s, which has been used to diagnose >50% carotid artery stenosis (CAS) in most vascular laboratories. This study is conducted to evaluate PSV >125 cm/s as a diagnostic tool for 50%> CAS. METHODS: The retrospective review was done for subjects, who had PSV >125 cm/s in carotid artery screening test in == Hospital from November 2008 to June 2011. The screening study was conducted to healthy senior volunteers to screen CAS. The subject who has PSV >125 cm/s was evaluated by carotid computed tomography (CT) scan. The clinical characteristics were surveyed. RESULTS: One hundred forty seven subjects were diagnosed with CAS using duplex scan from 1,953 subjects who underwent screening tests. Twenty eight with 33 lesions underwent carotid CT scan. There were 71% hypertension, 21% diabetes mellitus, 21% ischemic heart disease, 17% lipid disorder, and 67% smoking history. Seventeen lesions showed >50% CAS while 16 showed <50% CAS. The false positive rate was 49%. Its causes were severe tortuosity of carotid artery and extensive plaque calcification. CONCLUSION: The false positive rate of PSV >125 cm/s was 49% in this study. For diagnostic accuracy, diagnostic criteria should be established in each vascular lab.