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To test the hypothesis that sleep-related breathing disorder (SRBD) is associated with increasing severity of cardiovascular risk markers.A cross-sectional study of sleep laboratory patients.University Hospital Sleep Disorders Centre.We studied 591 patients referred for a sleep study, all of them without a history of systemic hypertension.Clinical interview, two unattended sleep studies, and assessment of office blood pressure, cholesterol concentration, alcohol and nicotine consumption and daytime blood gases.Post-hoc analysis of different cardiovascular risk markers: mean blood pressure, pulse pressure, and the type and grade of systemic hypertension.Patients were classified as normotensive (blood pressure < 140/90 mmHg, n= 228) or hypertensive (blood pressure ≥ 140/90 mmHg, n= 363) according to office blood pressure measurements. Mixed (systolic and diastolic) hypertension was the most common type of hypertension (n= 182), followed by isolated diastolic hypertension (n= 101), borderline isolated systolic hypertension (n= 70), and isolated systolic hypertension (n= 10). The frequency of mixed hypertension increased with SRBD activity (P< 0.05) and respiratory disturbance index (RDI; the number of breathing disorders per hour of estimated sleep time) was increased in those with mixed hypertension compared with those with normotension (24.8 compared with15.7;t test:P< 0.01). In hypertensive patients classified as having grades 1–3 of hypertension (n= 265, 80 and 18, respectively), there was a progressive increase in RDI (18.9, 27.2 and 30.3, respectively, P< 0.01). Mean blood pressure increased significantly with RDI. Pulse pressure increased significantly with age (P< 0.001), but was unrelated to the degree of SRBD.We conclude that mean blood pressure and the severity of hypertension, but not pulse pressure, increase with the severity of the SRBD.