ImportanceMinoritized racial and ethnic groups are generally more likely to experience sleep deficiencies. It is unclear how these sleep duration disparities have changed over recent years.ObjectiveTo determine 15-year trends in the racial and ethnic differences in self-reported sleep duration among adults in the US.DesignSerial cross-sectional study.SettingNational Health Interview Survey from years 2004–2018.Participants429,195 non-institutionalized adults.ExposuresSelf-reported race, ethnicity, household income, and sex/gender.Main OutcomesTemporal trends and racial/ethnic differences in short- and long-sleep duration (≤6 and ≥10 hours in a 24-hour period, respectively) and racial/ethnic differences in the relationship between sleep duration and age.ResultsThe study sample consisted of 429,195 individuals (mean age 46.5 [SE, 0.08] years; 51.7% female) of which 5.1% identified as Asian, 11.8% as Black, 14.7% as Latino/Hispanic, and 68.5% as White. In 2004, the adjusted estimated prevalence of short-sleep duration and long-sleep duration, respectively, were 31.3% and 2.5% among Asian individuals, 35.3% and 6.4% among Black individuals, 27.0% and 4.6% among Latino/Hispanic individuals, and 27.8% and 3.5% among White individuals. Over the study period, there was a significant increase in the short sleep prevalence among Black, Latino/Hispanic, and White individuals (P≤0.02 for each), whereas prevalence of long sleep changed significantly only among Latino/Hispanic individuals (−1.4 points, P=0.01). In 2018, compared with White individuals, short sleep prevalence among Black and Latino/Hispanic individuals was higher by 10.7 points and 2.6 points, respectively (P≤0.02 each), and long sleep prevalence among Black people was significantly higher by 1.4 points (P=0.01). These racial/ethnic disparities were the greatest among women and among those with middle/high household income. Over the study period, Black individuals younger than 60 years old had the highest prevalence of short sleep compared with those of the same age; and Black individuals had a higher long-sleep duration prevalence than White individuals across all age groups.ConclusionsFrom 2004 to 2018, the prevalence of unrecommended sleep duration was persistently higher among Black individuals. The Black-White disparities were highest among women, individuals who had middle or high income, and among young or middle-aged adults.KEY POINTSQuestionHow have racial and ethnic differences in self-reported sleep duration among US adults changed between 2004 and 2018?FindingsIn this serial cross-sectional study that included 429,195 adults, the prevalence of unrecommended sleep duration was persistently higher among Black individuals over the 15- year study period. These disparities were highest for Black women, Black individuals with middle or high income, and young and middle-aged Black adults.MeaningThere were marked racial and ethnic differences in sleep duration that persisted from 2004 to 2018, which may be contributing to health disparities.