OBJECTIVE To measure the independent association of sleep-disordered breathing (sleep apnea and habitual snoring) and hypertension in a healthy adult population. METHODS A cross-sectional study of blood pressure during wakefulness and sleep among participants with and without sleep-disordered breathing. METHODS Community-based study. METHODS 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. METHODS 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.