Sokol NA, et al. - This study was undertaken to ascertain if youth who used e-cigarettes in 2014-2018 would have likely been smokers in the period preceding e-cigarette availability. Assessing Monitoring the Future 12 ^th grade data (the USA, 2009-2018), researchers forecasted the prevalence of current smoking with logistic regression-derived propensity scores. Among non-smokers across smoking propensity tertiles, forecasted to observed smoking prevalence annually and prevalence of current e-cigarette use were compared. Observed smoking prevalence mirrored forecasted prevalence until 2014. The findings revealed that youth e-cigarette use has elevated rapidly, with a high prevalence among non-smoking youth. Nevertheless, the decline in current smoking among 12 ^th graders has accelerated since e-cigarettes have become available. This study’s findings demonstrate that e-cigarette use is largely concentrated among youth who share characteristics with smokers of the pre-vaping era, implying e-cigarettes may have replaced cigarette smoking.