Metabolic syndrome (MetSyn) may predispose to cardiovascular disease (CVD) by causing vascular dysfunction. This study aimed to determine the association of MetSyn with vascular function, as assessed by brachial artery flow-mediated dilatation (FMD) and hyperemic shear stress (HSS). A total of 1,417 male firefighters without established diabetes and CVD were classified for MetSyn, according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP) definition. MetSyn was present in 267 individuals (19%). Although FMD was lower in those with versus without MetSyn (8.1 ± 4.1 vs 8.7 ± 4.0%; p = 0.02), this was not significant after adjusting for baseline differences (age, smoking, and brachial artery diameter) ( p = 0.2). However, HSS was significantly lower in those with versus without MetSyn (72.0 ± 27.8 vs 80.9 ± 24.8 dyne/cm2; p < 0.001), and there was a significant inverse graded relationship with the number of NCEP criteria present (mean HSS for those with 0, 1, 2, 3, 4, and 5 criteria: 83.2 ± 22.5, 82.2 ± 24.7, 76.5 ± 27.2, 74.3 ± 27.4, 66.5 ± 28.4, 67.1 ± 27.6 dyne/cm2; p < 0.001 for trend). The individual NCEP criteria of abdominal obesity, systolic hypertension, and impaired fasting glucose were independent predictors for HSS. In conclusion, MetSyn was not associated with impaired FMD. Alternatively, HSS, a measure of microvascular function, was significantly lower in those with MetSyn. Thus, MetSyn may contribute to CVD by causing microvascular dysfunction.