Vaping has become an increasingly common mode of administration for marijuana among youth, but there are limited data on its prevalence. There is a need to better understand youth prevalence of past 30-day marijuana vaping and its predictors. Data were from a nationally representative sample of students from the Monitoring the Future survey in 2018 (N=9,131). This study examined past 30-day prevalence of marijuana vaping, and for a subset with complete data (n=5,755), the predictors of marijuana vaping among respondents asked about that behavior. Bivariate chi-square tests and multivariable logistic regression estimated the extent to which various factors were associated with marijuana vaping. These factors included the current use of various substances, school-related risk behaviors, attitude and risk behaviors related to substance use, and selected sociodemographic variables. Past 30-day prevalence of marijuana vaping was higher among 10th graders, male youth, and those in the Other race/ethnicity category. Students who engaged in current past 30-day alcohol use, cigarette use, binge drinking, and nonmedical use of prescription drugs had significantly greater odds of past 30-day marijuana vaping. Past 30-day use was more common among students with a lower perceived risk of marijuana use, those who claimed that it was easy to obtain a vaporizer or marijuana, students with a lower grade point average, and those with recent truancy. Past 30-day marijuana vaping is prevalent among U.S. students, and there are robust associations between use and school- and substance-related risk behaviors. These results suggest that the emergence of vaping products might redefine populations at risk, which should be taken into account by marijuana regulatory policies or prevention programs.