Although the prevalence of e]cigarette use among adolescents and young adults has caught up to or eclipsed that of combustible cigarette use, there is relatively little known about (a) the link between e]cigarettes and other substances and (b) the reasons underlying this increase in e]cigarette use. The current study addressed this research gap. Participants included an ethnically diverse sample of African-American, White, and Hispanic young adults (N = 662; 61 percent female) who were participating in an ongoing survey]based longitudinal study of health and risky behaviors. Hispanic, White, and male young adults reported significantly greater past year e]cigarette use compared to their African- American and female counterparts. Bivariate correlations showed that use of e]cigarettes was positively associated with use of combustible cigarettes, alcohol, marijuana, cocaine, amphetamines, inhalants, hallucinogens, ecstasy, and misuse of over]the]counter and prescription medications. Furthermore, e]cigarette users reported a higher prevalence of substance use relative to those who did not use e]cigarettes. The taste of e]cigarettes was identified as an important motive for use. Although the potential harm associated with e]cigarettes remains largely unknown, e]cigarettes appear to be a risk marker for the use of substances that are known to pose substantial health problems. Healthcare providers should screen for e]cigarette use, and youth substance-use prevention programs should target the reduction of e]cigarette use, with attention to addressing their taste appeal. (Publisher abstract modified)