Fantasy sports is a growing industry with a reported 56.8 million individuals participating in the United States and Canada alone in 2015. Whereas this activity has attracted considerable public attention, little research has examined its impact on adolescents in spite of their high rates of gambling. The current study examined the relationship between regular participation (more than once a month) in sport-relevant gambling activities among adolescents and those identified as being at-risk for a gambling problem. Questionnaire responses were collected from high school students (N = 6818; 49 % male) in Wood County, Ohio, United States. Statistical analyses revealed that regular involvement in sports betting, fantasy sports betting, and daily fantasy sports betting among adolescents was associated with a higher risk of gambling problems. Further, although males participate more frequently in these activities, females who participate have a stronger likelihood of being at-risk. Students aged 16–19 years old are at a higher risk for developing a gambling problem compared to younger adolescents when regularly engaging in sports-related gambling. Moreover, regularly participating in daily fantasy sports is the strongest predictor of at-risk gambling behavior in 13–15 year old students. A hierarchical logistic regression supports that controlling for gender and age, all forms of sport-relevant gambling activities are significant predictors of at-risk gambling. This study contributes to a more comprehensive understanding of the impact of sports betting and fantasy sports on adolescents and establishes an initial step for future studies to further investigate these relationships.