Insulin resistance is a relevant risk factor for the major cardiovascular events, caused by severe atherosclerotic involvement of coronary, cerebral and lower limb blood vessels. One of the alterations accounting for this increased cardiovascular risk is the impairment of platelet function, explained, at least in part, by the reduced sensitivity to the physiological and pharmacological anti-aggregating agents. In the first part of this review, we will focus our attention on the physiological mechanisms involved in the attenuation of platelet response and on their impairment in insulin resistance, considering in particular: i) the reduced sensitivity to insulin and other substances acting via intracellular cyclic nucleotides; ii) the altered intracellular ionic milieu with elevated cytosolic Ca(2+), iii) the increase of oxidative stress, which elicits isoprostane production from arachidonic acid. Therapeutic guidelines recommend a multifactorial prevention including antiplatelet drugs, even though the protective effect of antiplatelet therapy in both obese and type 2 diabetic patients has not been completely clarified so far. Furthermore, some reports show a decreased sensitivity to the platelet antiaggregating effect of acetylsalicylic acid in obesity and type 2 diabetes mellitus. These defects explain why antiplatelet therapy for both chronic atherosclerotic vascular disease and acute coronary syndromes should be specifically tailored in obese, insulin resistant subjects, especially in the presence of type 2 diabetes mellitus. Thus, in the second part of this review we performed a critical overview of the clinical trials on anti-aggregating agents carried out in subjects with metabolic syndrome and type 2 diabetes mellitus.