This study aims to: (1) describe trajectories in the likelihood of smoking by racial or ethnic group across the transition to adulthood, (2) identify the influence of achieved socioeconomic status (SES) and the nature and timing of adult role transitions, and (3) determine the extent to which achieved SES and adult roles mediate the effects of race and ethnicity on smoking. The analyses use U.S. longitudinal data from the National Longitudinal Study of Adolescent Health (Add Health), which follows a representative national sample over four waves and from ages 11–17 in 1994/95 to 26–34 in 2007/08. Growth curve models compare trajectories of smoking likelihood for white, black, Hispanic, Asian/Pacific Islander, and American Indian/Alaska Native individuals. While whites have higher rates of smoking than blacks and Hispanics during their teen years and 20s, blacks and Hispanics lose their advantage relative to whites as they approach and enter their 30s. American Indian/Alaska Natives show high rates of smoking at earlier ages and an increasing likelihood to smoke. Although life course transitions are influential for smoking prevalence in the overall U.S. population, SES and the nature and timing of adult role transitions account for little of the gap between whites and black, Hispanic, and American Indian/Alaska Native individuals. Racial and ethnic disparities in adult smoking are independent of SES and life transitions, pointing to explanations such as culturally specific normative environments or experiences of discrimination.