Oxidative stress is the result of the imbalance between pro-oxidant and antioxidant factors. The participation of oxidative stress in atherosclerosis (ATS) is reflected by lipid peroxidation which is a process initiated and maintained by oxygen reactive species generated by the aterogenic cells themselves. The endothelial aggression in ATS is accompanied by endothelial dysfunction, which is due to the neutralization of nitric oxide by superoxid anion. The key role in the onset and the development of the ATS lesions belongs to oxidated LDL-cholesterol that influence at different levels and by several mechanisms the ATS process. The neutralization of the toxic effects of free radicals is due to the endo and exogen antioxidant systems. It appears that the individual antioxidant status is influenced by environmental factors as well as by a genetic determinant. The antioxidant therapy, which is controversial at the moment, represents an associated therapy in endothelial dysfunction from ATS.