Obstructive sleep apnea (OSA) is independently associated with cardiovascular diseases, including myocardial infarction and stroke. OSA may promote atherosclerosis risk factors such as hypertension, diabetes and dyslipidemia and may have direct proatherogenic effects on the vascular wall. A growing number of studies have recently focused on the role of microparticles (MPs) in the atherogenic process. Case-control studies have shown that platelet-, endothelial- and leukocyte-derived MP levels are increased in OSA and that leukocyte-derived MP are released during the night in OSA. Furthermore, experimental evidence shows that MPs from OSA patients induce endothelial dysfunction. The objective of this prospective study is to evaluate the impact of increased levels of leukocyte derived MPs on the cardiovascular outcomes in patients with prevalent cardiovascular diseases investigated for OSA.