Little is known about the extent to which insufficient sleep affects the ability of U.S. adults to carry out daily activities. The National Sleep Foundation suggests that adults need 7-9 hours of sleep per night; shorter and longer sleep durations have been associated with increased morbidity and mortality. To assess the prevalence of short sleep duration (<7 hours on weekday or workday nights) and its perceived effect on daily activities, CDC analyzed data from the 2005-2008 National Health and Nutrition Examination Survey (NHANES). This report summarizes the results, which found that 37.1% of U.S. adults reported regularly sleeping <7 hours per night, similar to the 35.3% reporting <7 hours of sleep in a 24-hour period in another report using self-reported data. Short sleep duration was more common among adults aged 20--39 years (37.0%) or 40-59 years (40.3%) than among adults aged ≥60 years (32.0%), and more common among non-Hispanic blacks (53.0%) than among non-Hispanic whites (34.5%), Mexican Americans (35.2%), and persons of other races/ethnicities (41.7%). Among six sleep-related difficulties assessed, the most prevalent was not being able to concentrate on doing things, reported by 23.2% of U.S. adults. Perceived sleep-related difficulties were significantly more likely among persons reporting <7 hours of sleep than among those reporting 7-9 hours of sleep. Based on these findings, at least one third of U.S. residents do not get enough sleep on a regular basis, and this impairs their ability to perform daily tasks. Chronic sleep deprivation also has a cumulative effect on mental and physical well-being and can exacerbate chronic diseases.