Background The aim of the present study was to prospectively evaluate the sensitivity, specificity, positive and negative likelihood ratios (LR+, LR-) of the ankle - brachial index (ABI), using conventional digital subtraction angiography (DSA) as the reference standard, in the assessment of lower extremity arteries, and to research the threshold value of the ABI in diagnosing periphery arterial disease (PAD), as well as the relationship between the ABI value and stenosis in the artery of the lower extremity in Chinese high-risk cardiovascular patients. Methods and Results A total of 298 consecutive patients (199 men, 99 women, 64.9±11.3 years old) underwent conventional DSA and ABI measurement. Receiver operator characteristics (ROC) analysis was performed to assess possible threshold values that predict PAD in these patients. The greater the stenosis in the artery of the lower extremity, the lower the measured ABI value. DSA was used as the gold standard in defining lesions ≥30%, ≥50%, and ≥70% and the respective areas under the ROC curve were 0.786 (95% confidence interval (CI) 0.712, 0.860), 0.927 (95% CI 0.869, 0.984), and 0.963 (95% CI 0.927, 0.999). Conventional DSA was the gold standard in defining ≥50% luminal stenosis for the diagnosis of lower extremity PAD. The 0.95 is the overall cutoff of the ABI that was associated with 91% sensitivity, 86% specificity, 6.5 LR+ and 0.1 LR- for detection of hemodynamically significant stenosis (lesions ≥50%) in all 298 subjects (p<0.001). Conclusion The ABI value shows a decreasing tendency with increasing severity of stenosis in patients with PAD. ABI measurement is an accurate and reliable noninvasive alternative to conventional DSA in the assessment of lower extremity arteries and the cut-off of 0.95 is the threshold ABI value for detecting PAD in Chinese patients. (Circ J 2008; 72: 605 - 610)