Polysomnography is used to assess sleep quality and to gauge the functional impact of sleep disorders. In this study, data from the Sleep Heart Health Study (N = 2685; ages, 37-92 years) are used to assess the variation in sleep architecture across the population subgroups and to evaluate the extent to which sleep-disordered breathing contributes to poor sleep independent of other factors. Lighter sleep was found in men relative to women and in American Indians and blacks relative to other ethnic groups. Increasing age was associated with impaired sleep in men, with less consistent associations in women. Notably, women, compared with men, had, on average, 106% more slow wave sleep (Figure 1). Marked reductions in slow wave sleep with increasing age were seen in men and not women. Sleep-disordered breathing was associated with poorer sleep; however, these associations were generally smaller than associations with sex, ethnicity, and age. Current smokers had lighter sleep than former or never smokers. Little impact on sleep was associated with obesity. These data show that sleep quality varies with sex, age, ethnicity, and sleep-disordered breathing. Men, but not women, show evidence of poorer sleep with aging, suggesting important sex differences in sleep physiology.