Objective: Although obstructive sleep apnoea syndrome (OSAS) is accompanied by an increased atherosclerotic cardiovascular disease burden, its relationship with arterial stiffness is not yet well determined. We investigated whether essential hypertensive individuals with OSAS are characterized by increased arterial stiffness., Methods: Our study population consisted of 46 consecutive patients with newly diagnosed untreated stage I-II essential hypertension suffering from OSAS (35 men, aged 49 +/- 8 years) and 53 hypertensive individuals without OSAS, matched for age, sex, and smoking status. All subjects underwent polysomnography, echocardiography and aortic stiffness evaluation by means of carotid-femoral pulse wave velocity (c-fPWV) measurements., Results: Hypertensive subjects with OSAS [apnoea/hypopnoea index (AHI)>or =5] compared with hypertensive subjects without OSAS (AHI < 5) demonstrated increased levels of body mass index (31.4 +/- 4 versus 29.3 +/- 4 kg/m2, P = 0.015), office systolic/diastolic blood pressure (151/99 versus 145/94 mmHg, respectively, P < 0.05, for both cases) and relative wall thickness (RWT; 0.46 +/- 0.06 versus 0.42 +/- 0.07, P=0.010). Hypertensive subjects with OSAS compared with those without OSAS had significantly increased c-fPWV by 9% (8.56 +/- 0.49 versus 7.85 +/- 0.93 m/s, P=0.001) and this difference remained significant even after adjustment for confounders (P=0.04). In the total study population, c-fPWV was correlated with age (r=0.35, P=0.015), office systolic blood pressure (r=0.30, P=0.007), RWT (r=0.30, P=0.03), logAHI (r=0.389, P=0.0001) and minimum oxygen saturation (r=-0.418, P=0.0001)., Conclusions: OSAS has a significant incremental effect on aortic stiffening in the setting of middle-aged essential hypertensive subjects. This finding suggests that the presence of OSAS in a hypertensive patient accelerates vascular damage, increasing cardiovascular risk.