BackgroundSleep affects health. Sleep habits differ between population subgroups and may also differ between weekdays and weekends; however, these patterns are rarely described at the population level. PurposeTo investigate age and racial/ethnic differences in sleep duration and timing between weekdays (workdays) and weekends (non-workdays). MethodsA cross-sectional analysis of the US nationally representative data from the National Health and Nutrition Examination Survey among adolescents (16-19 years) and adults (≥20 years). ResultsData on 10069 individuals were analyzed (51% female), including 959 adolescents and 9110 adults. The hours per night of sleep were shorter during weekdays (7.6, 95%CI: 7.6 to 7.7) than on weekends (8.3, 95% CI: 8.3 to 8.2). Females slept shorter hours than males on weekdays (7.7 [95%CI, 7.7 to 7.8] vs. 7.5 [95%CI, 7.4 to 7.5]) and on weekends (8.5, [95%CI, 8.4 to 8.5] vs. 8.2 [95% CI, 8.1 to 8.2]). Non-Hispanic blacks (7.4, 95% CI: 7.4 to 7.5) reported the shortest weekdays sleep. With respect to sleep timing, comparing to weekdays, males reported 30-min delayed weekends bedtime (23:30 [IQR, 22:30-00:30] vs. 23:00 [IQR, 22:00-00:00]), whereas both sexes reported 1.5-hour delayed weekends wake-up time (male: 07:30 [IQR, 06:30-09:00] vs. 06:00 [IQR, 05:30-07:30]; female: 08:00 [IQR, 06:30-09:00] vs. 06:30 [IQR, 05:30-07:30]). The delayed weekend bedtime and wake-up times were observed in all racial/ethnic groups. ConclusionsIn the US population, sleep habits differed between weekdays and weekends. Shorter sleep hours and delayed sleep timing were noted and more apparent among racial/ethnic minorities of both sexes.