['To identify associations between sleep-disordered breathing (SDB) and arterial stiffness.', 'Nested cross-sectional study.', 'One hundred fifty-three participants (ages 45-77 years, 43% women) in the population-based Wisconsin Sleep Cohort. Eighty-three had SDB and were not using continuous positive airway pressure therapy.', 'Measurement of aortic pulse wave velocity (PWV) by arterial tonometry. Nocturnal polysomnography.', 'SDB was defined as an apnea-hypopnea index (AHI) > or = 5 events/hour of sleep. By study design those with SDB had higher mean (SD) AHI (17.6 [16.2] vs 2.2 [1.3] events/h), as well as lower average nocturnal O2 saturation (91.5 [2.1] vs 93.0 [1.4] %, P < 0.001) and larger waist circumference (102.5 [13.2] vs 92.5 [12.5] cm, P < 0.001), but they had similar central aortic systolic (122.8 [15.1] vs 119.1 [11.8] mm Hg, P = 0.100) and diastolic blood pressures (77.1 [9.4] vs 77.4 [8.6] mm Hg, P = 0.834), and PWV (9.06 [2.15] vs 8.51 [1.88] m/s; all P > 0.10). Markers of SDB that were correlated with PWV were nocturnal O2 saturation (r = -0.24, P = 0.004) and AHI (r = 0.18, P = 0.032); however, these associations were not statistically significant after adjustment. In subjects not on antihypertensive medications, a significant interaction between nocturnal O2 saturation and age was identified (beta = -0.019, P = 0.039), such that the effect of nocturnal oxygen O2 on PWV increased with age (adjusted R2 = 0.468).'] Are the effects of sleep-disordered breathing on arterial stiffness modulated by age?