RESULTS: 128 individuals included (15 controls, 22 with mild, 22 with moderate, and 69 with severe OSAS). The mean age was 51.6 ±11.9 years and 56.3% (72/128) of the study population was male. As expected, the prevalence of hypertension, diabetes and cardiovascular disease increased as the severity of OSAS increased. Endocan levels were significantly higher and FMD measurements were lower in patients with OSA compared to healthy controls. There was a positive correlation between AHI and serum endocan levels (r=0.73, p<0.0001) and there was a negative correlation between AHI and FMD (r= -0.57, p<0.0001). In addition, we observed a strong negative correlation between serum endocan level and FMD (r= -0.62, p<0.0001).