BackgroundAmong high school students, seniors report the highest levels of hazardous drinking behavior, including playing drinking games. Technology-based interventions are a promising approach for reducing hazardous drinking behavior among this age group. Objectives: This randomized controlled trial investigated the efficacy of the eCHECKUP TO GO, an online personalized feedback intervention, on reducing the frequency of playing drinking games, the number of drinks consumed while playing drinking games, and the number of drinks consumed on occasions when drinking games were played among high school seniors (ClinicalTrials.gov Identifier NCT03613818). Method: Participants were recruited from two high schools. Class periods were randomized to the intervention condition or an assessment-only control condition. Participants completed online surveys at baseline, 30-day, and 6-month assessments. The subsample in this study (N = 109) consisted of high-risk drinkers (i.e., students reporting binge drinking in the past two weeks at baseline). Results: We did not find any significant differences in frequency of playing drinking games between the intervention and control conditions. For number of drinks consumed, students in the intervention condition reported a significant reduction in the number of drinks consumed while playing drinking games (p < 0.01) and total number of drinks consumed on drinking game occasions (p < 0.04) at the 30-day follow-up relative to students in the control condition. Reductions within the intervention group were sustained at the 6-month follow-up. Conclusions: Results support the efficacy of the eCHECKUP TO GO for decreasing hazardous alcohol use among high school seniors.