In this issue of JAMA Pediatrics, Primack and colleagues1 show that adolescents and young adults who smoke electronic cigarettes (e-cigarettes) are much more likely than those who had not smoked e-cigarettes to progress to traditional combustible cigarette use. Among 694 youth who were not susceptible to cigarette use, after 1 year, 68.8% of e-cigarette users and only 18.9% of those who had not smoked e-cigarettes had smoked a traditional combustible cigarette.