Oxidative stress and inflammation are considered to play a pivotal role in vascular endothelial dysfunction by triggering activation of transcription factors, such as NF-κB, functionally dependent on cellular redox status. The anthocyanin cyanidin-3-O-glucoside (C3G), as well as other phytochemicals recognized as potent antioxidants and free radical scavengers, may act as modulators of gene regulation and signal transduction pathways. This study demonstrates that C3G is able to protect human endothelial cells against alterations induced by TNF-α, including the activation of NF-κB, increased gene expression of adhesion molecules, leukocyte adhesion to endothelium, and intracellular accumulation of H2O2 and lipid peroxidation byproducts. These observations contribute to provide a conceptual background for the understanding of the mechanisms underlying the role of C3G, as well as other dietary plant polyphenols, in the prevention of diseases associated with inflammation and oxidative stress, including atherosclerosis.