This review focuses on the link between diabetes mellitus and oxidative stress and, in particular, on the role that moderate wine consumption may play in preventing diabetic complications and the onset of diabetes. With this aim, a search of PubMed was carried out for literature published up to March 2003. In diabetes mellitus, oxidative stress results both from exposure to hyperglycaemia through glycoxidation and sorbitol system activation, and from functional limitation of the hexose monophosphate shunt, leading to a decrease in glutathione synthesis. Oxidative stress alters the plasma lipoprotein profile (particularly low-density lipoproteins), the coagulative parameters (with an increased thrombotic risk), the endothelium (with a decrease in prostacyclin synthesis and an increase of thromboxane production) and the cell membranes (which undergo peroxidation). In diabetic patients, an altered oxidative pattern is present not only in the fasting state but also especially after food intake. In particular, food intake induces a decrease in the total radical-trapping antioxidant parameter (TRAP) and an elevation of hydroperoxides and thiobarbituric acid reactive substances (TBARS). Previously several clinical trials tried to improve the diabetic oxidative status using alpha-tocopherol, ascorbic acid and beta-carotene supplementation. Some authors found, in normal subjects, a reduction of hydroperoxides postprandially when the meal included red wine. Other authors showed that the oxidative pattern present in type 2 diabetic patients was mitigated by red wine. These actions may reduce cardiovascular risk. Moreover, an inverse relationship was observed between alcohol consumption and the incidence of type 2 diabetes; this relationship was valid for a light to moderate intake and it seemed to depend on drinking regularly and to be independent of the type of alcoholic beverage. In conclusion, moderate and regular wine consumption could ameliorate the diabetic oxidative status. This lifestyle measure might contribute to preventing diabetic complications and the onset of diabetes.