OBJECTIVE: To measure the independent association of sleep-disordered breathing (sleep apnea and habitual snoring) and hypertension in a healthy adult population. DESIGN: A cross-sectional study of blood pressure during wakefulness and sleep among participants with and without sleep-disordered breathing. SETTING: Community-based study. PARTICIPANTS: 147 men and women, aged 30 to 60 years, selected from Wisconsin State employees enrolled in the Wisconsin Sleep Cohort Study, an ongoing, prospective, epidemiologic study of sleep-disordered breathing. MEASUREMENTS: Sleep and medical history interview, nocturnal polysomnography, and 24-hour ambulatory blood pressure monitoring in all participants. RESULTS: Mean blood pressures were significantly higher among participants with sleep apnea (> or = 5 apneas or hypopneas per hour of sleep) compared with those without (131/80 +/- 1.7/1.1 mm Hg compared with 122/75 +/- 1.9/1.2 mm Hg during wakefulness and 113/66 +/- 1.8/1.1 mm Hg compared with 104/62 +/- 2/1.3 mm Hg during sleep, respectively; P < 0.05). The variability of the blood pressure during sleep was significantly greater in participants with sleep apnea or a history of snoring compared with those without (P < 0.05). After controlling for obesity, age, and sex, sleep apnea was significantly associated with hypertension in a dose-response fashion, with odds ratios ranging from 2.0 for 5 apneic or hypopneic episodes per hour of sleep to 5.0 for 25 apneic or hypopneic episodes. CONCLUSIONS: Our data indicate an association between hypertension and sleep apnea independent of obesity, age, and sex in a nonselected, community-based adult population.