ObjectiveTo systematically compare midlife mortality patterns in the United States across racial and ethnic groups during 1999-2016, documenting causes of death and their relative contribution to excess deaths.DesignTrend analysis of US vital statistics among racial and ethnic groups.SettingUnited States, 1999-2016.PopulationUS adults aged 25-64 years (midlife).Main outcome measuresAbsolute changes in mortality measured as average year-to-year change during 1999-2016 and 2012-16; excess deaths attributable to increasing mortality; and relative changes in mortality measured as relative difference between mortality in 1999 versus 2016 and the nadir year versus 2016, and the slope of modeled mortality trends for 1999-2016 and for intervals between joinpoints.ResultsDuring 1999-2016, all cause mortality in midlife increased not only among non-Hispanic (NH) whites but also among NH American Indians and Alaskan Natives. Although all cause mortality initially decreased among NH blacks, Hispanics, and NH Asians and Pacific Islanders, this trend ended in 2009-11. Drug overdoses were the leading cause of increased mortality in midlife in each population, but mortality also increased for alcohol related conditions, suicides, and organ diseases involving multiple body systems. Although midlife mortality among NH whites increased across a multitude of conditions, a similar trend affected non-white populations. Absolute (year-to-year) increases in midlife mortality among non-white populationsoften matched or exceeded those of NH whites, especially in 2012-16, when the rate of increase intensified for many causes of death. During 1999-2016, NH American Indians and Alaskan Natives experienced large increases in midlife mortality from 12 causes, not only drug overdoses (411.4%) but also hypertensive diseases (269.3%), liver cancer (115.1%), viral hepatitis (112.1%), and diseases of the nervous system (99.8%). NH blacks experienced increased midlife mortality from 17 causes, including drug overdoses (149.6%), homicides (21.4%), hypertensive diseases (15.5%), obesity (120.7%), and liver cancer (49.5%). NH blacks also experienced retrogression: after a period of stable or declining midlife mortality early in 1999-2016, death rates increased for alcohol related liver disease, chronic lower respiratory tract disease, suicides, diabetes, and pancreatic cancer. Among Hispanics, midlife mortality increased across 12 causes, including drug overdoses (80.0%), hypertensive diseases (40.6%), liver cancer (41.8%), suicides (21.9%), obesity (106.6%), and metabolic disorders (60.0%). Retrogression also occurred in this population; after a period of declining mortality, death rates increased for alcohol related liver disease, mental and behavioral disorders involving psychoactive substances, and homicides. NH Asians and Pacific Islanders were least affected by this trend but also experienced increases in midlife mortality from drug overdoses (300.6%), alcohol related liver disease (62.9%), hypertensive diseases (28.3%), and brain cancer ...