Objective To observe the serum cortisol level in ischemic stroke patients with obstructive sleep apnea syndrome (OSAS),and discuss the influence factors and its correlation with severity of cerebral infarction.Methods Two hundred ischemic stroke patients with onset of 6 h to 3 weeks,admitted to our hospital from July 2015 to April 2017,were recruited;all patients were monitored with polysomnography.According to apnea hypopnea index (AHI),all patients were divided into ischemic stroke without OSAS group (AHI＜5/h,n=89) and ischemic stroke with OSAS group (AHI≥ 5/h,n=111).Moreover,according to AHI,patients from ischemic stroke with OSAS group were divided into three subgroups,namely,mild subgroup (5/h ≤AHI＜15/h),moderate subgroup (15/h ≤AHI＜30/h) and severe subgroup (AHI ≥30/h).According to National Institutes of Health Stroke Scale (NIHSS) scores,all subjects were divided into a group of NIHSS scores no more than 10 and a group of NIHSS scores＞10.The general clinical data,biochemical indices,early morning blood pressure,serum cortisol level and sleeping parameters were detected and compared among the groups,and the main factors affecting serum cortisol levels were identified by multivariate linear regression analysis.Results (1) The serum cortisol level in ischemic stroke with OSAS patients ([195.41±75.31] μg/L) was significantly higher than that of ischemic stroke without OSAS patients ([158.65±77.28] μg/L,P＜0.05);the serum cortisol level in ischemic stroke with mild OSAS subgroup ([227.32±75.12] μg/L) was significantly increased as compared with that in the ischemic stroke with moderate OSAS subgroup and ischemic stroke with severe OSAS subgroup ([191.27±71.50] μg/L and [175.21±75.13] μg/L,P＜0.05).(2) The serum cortisol level of group of NIHSS scores＞10 was significantly higher than that of group of NIHSS scores ≤ 10 (P＜0.05).(3)AHI,NIHSS scores,longest duration of apnea,and lowest blood oxygen saturation at night had significant effects on serum cortisol levels.Serum cortisol levels increased with AHI (β=89.984,95％CI:71.325-108.644,P=0.000) and NIHSS scores (β=0.923,95％CI:0.377-1.468,P=0.001),increased with the longest sleep apnea (β=0.804,95％CI:0.262-1.325,P=0.000),and decreased with the lowest blood oxygen saturation at night (β=-0.709,95％CI:-0.290--0.041,P=0.000).Conclusion The serum cortisol level in cerebral infarction patients with OSAS was increased,and the higher the severity of cerebral infarction and OSAS is,the higher the serum cortisol level is.