Abstract Objective: We investigated whether essential hypertensive (EH) individuals with obstructive sleep apnoea syndrome (OSAS) are characterized by increased arterial stiffness, such as carotid intima- media thickness (CIMT), brachial ankle pulse wave velocity (baPWV) and coronary artery calcification score (CACS). Methods: Our study population consisted of 80 consecutive patients with newly diagnosed untreated essential hypertension suffering from OSAS and 82 hypertensive individuals without OSAS, matched for age, sex, and smoking status. All subjects underwent polysomnography (PSG) and arterial stiffness evaluation by means of CIMT, baPWV and CACS measurements. Results: Hypertensive subjects with OSAS [apnoea/hypopnoea index (AHI) ≥5] compared with hypertensive subjects without OSAS (AHI < 5) demonstrated decreased levels of minimum oxygen saturation (SaO2) (75.6±4.3 versus 90.2±1.0, P = 0.02), and increased percentage of SaO2 less than 90 percentage (29.2±1.6 versus 0±0, P = 0.01). Hypertensive subjects with OSAS compared with those without OSAS had significantly increased CIMT (1.29±0.32 versus 1.03±0.25mm, P = 0.03), baPWV (1484.56±103.42 versus 1251.26±84.46, m/s, P=0.01) and CACS (157.85± 204.63 versus 62.58± 102.47, P = 0.02) and this difference remained significant even after adjustment for confounders (all P≤0.05). In hypertensive subjects with OSAS , CIMT, baPWV and CACS were positive correlated with AHI (r=0.287, 0.242 and 0.278 , respectively, all P≤0.05). Conclusions: OSAS has a significant aggravated effect on arterial stiffening in the setting of essential hypertensive subjects. This finding suggests that the presence of OSAS in a hypertensive patient accelerates vascular damage, increasing cardiovascular risk.