It has been shown that elevated extra- and intra-cellular glucose concentrations result in an oxidative stress, which is defined as an imbalance between prooxidants and antioxidants. Several mechanisms seem to be involved in the genesis of this oxidative stress, which has been reported both in experimental diabetes in animals and in type 1 and type 2 diabetic patients: glucose autoxidation, protein glycation and formation of advanced glycation endproducts, and the polyol pathway. Reciprocally, oxidative stress is involved in the origin of type 1 diabetes, especially via the apoptosis of pancreatic beta-cells, as well as insulin resistance in type 2 diabetes. Glucose control plays an important role in the prooxidant/antioxidant balance. Macromolecules such as molecules of extracellular matrix, lipoproteins and deoxyribonucleic acid are also damaged by free radicals in diabetes mellitus. A supplementation with antioxidants has been proposed as a complementary treatment, and some antidiabetic agents may by themselves have antioxidant properties independently of their role on glucose control. The aim of this paper was to review the consequences of the diabetic status on the oxidant/antioxidant balance.