Although the link between obstructive sleep apnea syndrome and risk for cardiovascular disorders has yet to be fully described, the hypothetical involvement of endothelial dysfunction is pathophysiologically plausible. In order to test this hypothesis, we measured plasma levels of endothelial markers in 82 male subjects (41 subjects with obstructive sleep apnea syndrome and a 41-subject control group). Obstructive sleep apnea syndrome patients presented higher circulating levels of intercellular cell adhesion molecule-1, E-selectin, and endothelin-1 than the control group. On the other hand, no differences were found in the von Willebrand factor. Levels of E-selectin and intercellular cell adhesion molecule-1 were significantly correlated to total oxygen desaturation. However, no significant correlation was found in either endothelin-1 or von Willebrand factor. We conclude that obstructive sleep apnea syndrome is associated with changes in levels of adhesion molecules, and that this could be the result of obstructive sleep apnea syndrome-induced hypoxia.