Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. We prospectively evaluated endothelial function by assessing flow-mediated dilatation (FMD) of the brachial artery in patients with biopsy-proven NAFLD. This prospective study included 139 patients (50 healthy controls, 47 patients with steatosis and 42 patients with steatohepatitis), all of whom were nondiabetic. Patients with long-standing or uncontrolled hypertension, smokers, and morbidly obese patients were excluded. The medians (ranges) for vascular FMD in the steatohepatitis, steatosis, and control groups were 6% (0-37.5%), 10.8% (0-40%) and 13.6% (0-50%), respectively. The control group had a higher average FMD than the NAFLD group (15.13% vs 10.46%), and statistical significance was reached when the control and steatohepatitis groups were compared (13.6% vs 6%, p = 0.027). Average alanine aminotransferase was significantly higher in the steatohepatitis group than in the steatosis and control groups (54 (U/L) vs 31 (U/L), p = 0.008). Cholesterol levels were similar between all groups. In the multivariate analysis, FMD (OR = 0.85, p = 0.035) and high triglycerides (OR = 76.4, p = 0.009) were significant predictors of steatohepatitis. In the absence of major cardiac risk factors, we demonstrated better endothelial function in healthy controls, evidenced by a higher FMD of the brachial artery than that of patients with steatohepatitis.