Background Concomitant prevalence of obstructive sleep apnea hypopnea syndrome (OSAHS) and pulmonary embolism (PE) was strikingly high.We studied patients with PE to determine whether those who had OSHAS required higher warfarin doses than those without OSHAS to achieve a therapeutic international normalized ratio (INR).Methods By using Computer tomographic pulmonary angiography or pulmonary angiography, weidentified and recruited 97 PE patientsand all underwent polysomnography.Warfarin was initiated at a dose of 3mg/day and modified to adjust the INR to the range of 2.0 to 3.0.Results Thirty-two OSAHS patients took a much higher mean dose of warfarin than their non-OSAHS counterparts (5.01 mg VS 3.61 mg, P <.001).This difference still existed between the two groups after adjusting for covariates (achieved INR value and weight).Logistic analysis suggested that OSAHS was an independent risk factor for high dose warfarin (OR 5.715, P <.001).On admission, OSAHS patients had a lower mean value of INR and prothrombin timebut higher plasminogen (PLG) activity compared to non-OSAHS patients.Other coagulating indexes were not significantly different between the two groups.Except for the PLG activity (r=.273, P =.026), the correlation between the warfarin dose and the baseline coagulating indexes wasnt significant.Conclusions PE patients complicated by OSAHS need a higher dose of warfarin than non-OSAHS patients to achieve an INR in the therapeutic range.Hypercoagulation is one, but not a critical, reason for the higher warfarin dosage.