A key developmental period for alcohol misuse is emerging adulthood (roughly ages 18–25). Personalized Feedback Interventions (PFI) are effective in reducing alcohol-related harmin college populations, however little research has evaluated PFIs given during high school.Moreover, cultural differences influence both alcohol misuse and response to interventions. The purpose of this study is to evaluate the efficacy of a web-based PFI given to high school seniors (ages 17-19) in the USA and Sweden. 1181 participants (42.3%male; 28.3%risky drinkers based on AUDIT-C) in the USA and 2171 in Sweden (44.1%male; 52.3% risky drinkers based on AUDIT-C) were assessed during their high school senior year. Approximately 1/3 were randomized to receive PFI. Approximately 1 week after viewing the PFI, participants were asked to complete a post-feedback satisfaction survey (3 subscales: information motivated change, shared information with friends, information was educational), and their “stage” on the readiness to change scale. Results showed 1) information motivated change subscale was associated with increases in contemplation and action stages of change and decreases in precontemplation; Swedish participants and those with higher AUDIT-C scores had lower scores; (2) USA sample was less likely to share information with friends; those with higher AUDIT-C scores were more likely to share information with friends; and (3) those with higher AUDIT-C scores were less likely to find information educational. Participants completed 6- and 12- month follow up surveys. After controlling for key baseline variables and using appropriate distributions for analyses, 6 month outcomes from 2236 participants (852 in USA; 1384 in Sweden; 731 received PFI), found those who received PFI drank significantly less alcohol per occasion (typical and peak), had lower blood alcohol concentration (typical and peak) and drank on fewer occasions than those who did not receive the PFI (effect size range: d = .12 to d = .22). There were no significant effects of PFI on alcohol-related problems or readiness to change and no significant interactions between country of residence and intervention on drinking outcomes. Results suggest web-based PFIs given during senior year of high school are efficacious in reducing alcohol use during transition to adulthood. Twelve-month outcomes and mediators will also be presented. This research was supported by NIAAA # 5R01AA018276 awarded to Drs. Larimer & Berglund.