Endothelial cell injury and dysfunction are the major triggers of pathophysiological processes leading to cardiovascular disease. Endothelial dysfunction (ED) has been implicated in atherosclerosis, hypertension, coronary artery disease, vascular complications of diabetes, chronic renal failure, insulin resistance and hypercholesterolemia. Although now recognized as a class of physiological second messengers, reactive oxygen species (ROS) are important mediators in cellular injury, specifically, as a factor in endothelial cell damage. Uncontrolled ROS production and/or decreased antioxidant activity results in a deleterious state referred to as “oxidative stress”. A candidate factor in causing ROS production in endothelial cells is tumor necrosis factor alpha (TNF-α), a pleiotropic inflammatory cytokine. TNF-α has been shown to both be secreted by endothelial cells and to induce intracellular ROS formation. These observations provide a potential mechanism by which TNF-α may activate and injure endothelial cells resulting in ED. In this review, we focus on the relationship between intracellular ROS formation and ED in endothelial cells or blood vessels exposed to TNF-α to provide insight into the role of this important cytokine in cardiovascular disease.