Obstructive sleep apnea syndrome (OSAS) is an important risk factor in cardiovascular disorders. Although the precise mechanism remains to be described, hypercoagulability seems to be involved. To test the presence of decreased fibrinolysis, we measured plasma levels of plasminogen activator inhibitor-1 (PAI-1) in 96 male subjects (32 subjects with OSAS, 32 subjects with both OSAS and hypertension, and a 32 subjects in the control group). All subjects completed a sleep questionnaire and underwent a general physical examination, biochemistry test, and polysomnography study. Patients and control subjects had similar baseline clinical characteristics for age, gender, smoking habit, and levels of cholesterol and triglycerides. Patients with OSAS presented significantly higher circulating levels of PAI-1 compared with the control group, and the difference was even more marked in patients with both OSAS and hypertension. OSAS patients presented a significant inverse correlation between PAI-1 levels and apnea-hypopnea index (r= -0.71, p<0.001). In conclusion, OSAS patients presented higher circulating levels of PAI than the control group, which was even greater when patients had associated hypertension.