The relationships between metabolic disorders and cardiovascular diseases are very strong. Hypercholesterolaemia and diabetes mellitus, for instance, are well-known risk factors. The multifaceted metabolic syndrome or syndrome X, originally described by Reaven in 1988, comprises several abnormalities which are associated to insulin resistance and compensatory hyperinsulinaemia. Syndrome X results in an increased vascular risk by at least two mechanisms. On the one hand, it favours atherosclerosis and is associated to angiographic lesions, especially in the coronary arteries. On the other hand, it is associated to endothelial dysfunction which may contribute to myocardial ischaemia even in presence of angiographically normal arteries, a phenomenon named also syndrome X by the cardiologists. Thus, metabolic syndrome X and cardiological syndrome X are very close and syndrome X may be considered as a crossing between metabolic disorders and cardiovascular diseases.