Aims: To investigate whether e-cigarette and cigarette susceptibility predict e-cigarette and cigarette use among American youth 1 year later. Design and Setting: Longitudinal data from the Population Assessment of Tobacco and Health (PATH) Study—a four-stage, stratified probability cohort study of youth (12–17 years old) sampled from the United States civilian, non-institutionalized population. Multivariable logistic regression was used to estimate the association between initial product-specific susceptibility and subsequent cigarette smoking and e-cigarette use while controlling for sociodemographic characteristics, exposure to nicotine users, and behavioral risk factors. Participants: The sample included 8841 adolescent never nicotine users at initial survey who participated in both wave 4 (2016–2017) and wave 4.5 (2017–2018) of PATH. Measurements: We measured cigarette and e-cigarette susceptibility (defined as a lack of a firm commitment to not use cigarettes or e-cigarettes) among never nicotine users at baseline (wave 4) as well as cigarette and e-cigarette use at 12-month follow-up (wave 4.5). Findings: Youth e-cigarette susceptibility was statistically significantly (P < 0.05) associated with e-cigarette use 1 year later, for both past 12-month (adjusted odds ratio [aOR], 2.99; 95% CI, 2.29–3.90) and past 30-day e-cigarette use (aOR, 2.73; 95% CI, 1.78–4.16), but not with cigarette smoking (aOR, 1.05; 95% CI, 0.64–1.73 for past 12-month smoking and aOR, 0.65; 95% CI, 0.29–1.45 for past 30-day smoking. Smoking susceptibility predicted subsequent smoking in the past 12 months (aOR, 1.82; 95% CI, 1.09–3.03) and past 30 days (aOR, 3.32; 95% CI (1.33–8.29), but not e-cigarette use in the past 12 months (aOR, 0.96; 95% CI, 0.77–1.19) or past 30 days (aOR, 1.11; 95% CI, 0.82–1.51). Conclusion: E-cigarette and cigarette susceptibility measures appear to predict product-specific use among youth 1 year later.