Background: Noninvasive methods are needed for the identification of women at highest risk for coronary artery disease (CAD) who might benefit most from aggressive preventive therapy. Identification of brachial artery atherosclerosis, which correlates with coronary artery atherosclerosis, may be useful to estimate or stratify CAD risk. Because atherosclerosis disrupts the arterial architecture that regulates vessel size, we hypothesized that noninvasively measured large brachial artery diameter is a manifestation of atherosclerosis that is associated with angiographic CAD in women with chest pain. Methods: We examined 376 women (mean age, 57.1 years) with chest pain in the National Heart, Lung, and Blood Institute's Women's Ischemia Syndrome Evaluation study who underwent B-mode ultrasound scan measurement of brachial artery diameter at rest and during hyperemic stress (to quantify flow-mediated dilation), quantitative coronary angiography, and risk factor assessment. Results: Large resting brachial artery diameter was associated with significant angiographic CAD (3.90 ± 0.79 mm vs 3.52 ± 0.59 mm in women with CAD vs no CAD; P < .001). Impaired flow-mediated dilation, which correlated with resting diometer (r = -0.17; P = .001), was weakly associated with significant CAD (2.74% ± 7.11% vs 4.48% ± 9.52% in CAD vs no CAD; P = .046). After adjustment for age, body size, and CAD risk factors, women with large resting brachial artery diameters (>4.1 mm) had 3.6-fold increased odds (95% confidence interval, 1.8 to 7.1; P < .001) of significant angiographic CAD compared with those with small brachial arteries (≤3.6 mm). Conclusion: Large resting brachial artery diameter is an independent predictor of significant CAD in women with chest pain. Therefore, a simple ultrasonographic technique may be useful in the identification of women with chest pain who are at increased risk for CAD.