Several studies have shown the occurrence of an independent association between obstructive sleep apnea syndrome (OSAS) and cardiovascular disease, including arterial hypertension, ischemic heart disease, and stroke. The pathogenesis of the cardiovascular complications of OSAS is still poorly understood, however. Several mechanisms are likely to be involved, including sympathetic overactivity, selective activation of inflammatory molecular pathways, endothelial dysfunction, abnormality in the process of coagulation, and metabolic dysregulation. The latter may involve insulin resistance and disorders of lipid metabolism. The aim of this review, which reports the data presented at a workshop jointly endorsed by the European Society of Hypertension and by the European Union COST action on OSAS (COST B26), is to critically summarize the evidence available to support an independent association between OSAS and cardiovascular disease.