The aim of our study was to evaluate if endothelial-dysfunction (ED) occurs in patients with primary Sjogren syndrome (pSS) and whether it is associated with the disease characteristics and activity. A total of 46 patients with pSS and 30 controls, without known cardiovascular disease, were enrolled in this study. A flow-mediated-dilation (FMD) of the brachial artery, plasma concentrations of the nitric oxide (NO) metabolic pathway (ADMA, L-arginine, SDMA, cGMP), and markers of endothelial inflammatory function (PAI-1, sE-selectin) and angiogenesis (angiostatin, VEGF) were analyzed. The FMD was significantly lower in pSS patients (7.56 ± 3.08 vs. 10.91 ± 1.02%, p = 0.043) and positively correlated with the Ro/SS-A-antibodies (r = 0.34, p = 0.03), pulmonary involvement (r = 0.52, p = 0.001) and inversely with ADMA (r = −0.35, p = 0.04). Plasma ADMA, L-arginine and angiostatin levels were significantly higher in pSS patients (0.39 ± 0.08 vs. 0.36 ± 0.06 µmol/L, p = 0.05; 29.07 ± 6.7 vs. 25.4 ± 5.23 µmol/L, p = 0.01; 152.25 ± 60.99 vs. 120.07 ± 38.7 pg/mL, p = 0.0, respectively). ADMA was associated with ESSDAI (r = 0.33, p = 0.02), SCORE (r = 0.57, p = 0.00003) and focus score (r = 0.38, p = 0.04). In the multiple regression analysis, the ESSDAI was significantly and independently associated with plasma ADMA levels (β = 0.24, p = 0.04). Moreover, plasma cGMP concentrations were negatively correlated with the disease duration (r = −0.31, p = 0.03). Endothelial function is impaired in patients with pSS and associated with the measures of disease activity, which supports the key-role of inflammation in developing and maintaining accelerated atherosclerosis.