The high availability and accessibility of online gambling have recently caused public concern regarding the potential increase of gambling-related problems among young people. Nonetheless, few studies among adults and none among adolescents have explored specific characteristics of gamblers as a function of gambling venues to date. This study sought to analyze the prevalence of gambling among a sample of adolescents in the last year, as well as sociodemographic and gambling-related characteristics as possible predictors of at-risk and problem gambling. The sample comprised 1313 adolescents aged 14–18 years. Participants were asked to respond to several questions regarding their gambling behavior. Chi square and ANOVA tests were performed in order to explore differences between groups, and a set of multinomial regressions established significant severity predictors. The prevalence of at-risk and problem gambling was 4 and 1.2 %, respectively. Regression analyses showed that having a relative with gambling problems predicted at-risk gambling. Both living with only one parent or not living with parents at all, and the prevalence of Electronic Gambling Machines in the last year were associated with problem gambling. Mixed-mode gambling was a predictor of both at-risk and problem gambling. Our findings extend previous research on gambling among adolescents by exploring gambling behavior according to different modes of access. Although the prevalence of exclusive online gambling among the total sample was low, these results support the need to consider specific subgroups of gamblers and their concrete related features when conducting both indicated prevention and treatment protocols for adolescents.