This paper investigates hypotheses regarding the cause of the recent apparent increase in young adult smoking, compares trends in smoking among young adults with trends in the use of other substances, and considers the implications for youth tobacco control research and policy. Time series analyses of national data suggest that the recent observed increase in smoking among young adults is primarily an artefact of the almost simultaneous increase in smoking among high school students. In addition, however, it also appears that there have been real changes in smoking patterns among young adults. While many questions remain regarding recent trends in tobacco and other drug use among adolescents and young adults, what is known leads to a clarion call for increased intervention and policy action for the prevention and control of tobacco use among young adults in the USA.