Sleep duration is associated with cardiovascular disease and diabetes risk factors, depression, automobile and workplace accidents, and prospective mortality. Little is known, however, about sleep patterns in the US population. The 2004-2007 National Health Interview Survey-Sample Adult Files provide nationally representative data for 110,441 noninstitutionalized US adults aged 18 years or older, and multinomial logistic regression examines whether variables in 5 domains-demographic, family structure, socioeconomic, health behavior, and health status-are associated with long or short sleep duration. Being older, non-Hispanic black, or a current or former smoker; having low levels of education, income, or few income sources; consuming few or numerous drinks in a week; or reporting cardiovascular disease, diabetes, depression, underweight, or activity limitations is associated with increased odds of both long and short sleep duration. Other variables are associated with shorter (e.g., living with young children, being unmarried, working long hours, more frequent binge drinking) or longer (e.g., being younger, Mexican American, pregnant, or having low levels of physical activity) sleep hours. The authors identify numerous risk factors for long and short sleep; many of those variables are potential confounders of the relation between sleep hours and other health outcomes.