The correlates and consequences of pulmonary hypertension (PH) associated with obstructive sleep apnea (OSA) are poorly understood. Patients undergoing pulmonary artery catheterization within 6 months of an overnight polysomnography showing OSA were included in the present analysis. A total of 83 patients with complete data were analyzed (no PH, n = 25 [30%]; PH, 58 [70%]; of these, 18 had a pulmonary capillary wedge pressure of <15 mm Hg). No significant differences were observed between the PH and no PH groups regarding age or apnea-hypopnea index. The correlates of PH were elevated right ventricular systolic pressure (p <0.001), body mass index (p = 0.026), female gender (p = 0.01), nocturnal desaturation (82% vs 18%), and forced vital capacity <70% (p = 0.04) on univariate analysis and female gender (p = 0.03), age <49 years (p = 0.02), body mass index of > or =26 kg/m(2) (p = 0.08), and right ventricular systolic pressure of > or =30 mm Hg (p <0.001) on multivariate analysis. Patients with PH had a lower 6-minute walk distance (285.5 +/- 122 m vs 343 +/- 213 m, p = 0.4). The survival rate at 1, 4, and 8 years for patients with PH was 93%, 75%, and 43% compared to 100%, 90%, and 76% for patients without PH, respectively. Patients with severe PH (n = 27; 33%) had more nocturnal desaturation (p = 0.045), worse pulmonary hemodynamics, and greater mortality (37%) than the groups with mild or moderate PH (16%) or no PH (16%). In conclusion, our results have shown that, although generally mild to moderate, severe PH can occur in patients with OSA. Female gender, younger age, obesity, and nocturnal desaturation were associated with PH. PH can cause functional limitations and increased mortality in patients with OSA.