PURPOSE:COVID-19 morbidity and mortality reports in the U.S. have not included findings specific to young adults. The Centers for Disease Control and Prevention provides a list of conditions and associated behaviors, including smoking, conferring vulnerability to severe COVID-19 illness regardless of age. This study examines young adults' medical vulnerability to severe COVID-19 illness, focusing on smoking-related behavior. METHODS:A young adult subsample (aged 18-25 years) was developed from the National Health Interview Survey, a nationally representative data set, pooling years 2016-2018. The medical vulnerability measure (yes vs. no) was developed, guided by the Centers for Disease Control and Prevention medical indicators. The estimates of medical vulnerability were developed for the full sample, the nonsmoking sample, and the individual risk indicators. Logistic regressions were conducted to examine differences by sex, race/ethnicity, income, and insurance. RESULTS:Medical vulnerability was 32% for the full sample and half that (16%) for the nonsmoking sample. Patterns and significance of some subgroup differences differed between the full and the nonsmoking sample. Male vulnerability was (33%) higher than female (30%; 95% CI: .7-.9) in the full sample, but lower in nonsmokers: male (14%) versus female (19%; 95% CI: 1.2-1.7). The white subgroup had higher vulnerability than Hispanic and Asian subgroups in both samples-full sample: white (31%) versus Hispanic (24%; 95% CI: .6-.9) and Asian (18%; 95% CI: .4-.5); nonsmokers: white (17%) versus Hispanic (13%; 95% CI: .06-.9) and Asian (10%; 95% CI: .3-.8). CONCLUSIONS:Notably, lower young adult medical vulnerability within nonsmokers versus the full sample underscores the importance of smoking prevention and mitigation.