Diabetes mellitus is characterized by fasting hyperglycaemia and the development of chronic vascular complications. While microvascular disease has been strongly related to glycaemic control, the major cause of mortality in diabetes is due to macrovascular disease affecting the cardiac and cerebrovascular circulations, which appear to have a more complex pathogenesis. Diabetes is associated with a 3-5-fold increase in death from myocardial infarction and similar figures pertain to stroke. The processes involved in atherothrombotic disease are complex and include variation in lipid metabolism, vascular responses, cell/cell interactions, and in the fluid and cellular phases of coagulation and fibrinolysis. The complex interactions between all of these processes are crucially altered by the metabolic milieu that characterizes diabetes mellitus, tipping the delicate balance towards atheroma formation, platelet aggregation and thrombus formation. This article will review these mechanisms and the effects of diabetes in the pathogenesis of vascular disease.