We tested whether a brief motivational interview (MI) would reduce alcohol-related consequences and use among adolescents treated in an emergency department (ED) after an alcohol-related event. Patients aged 13 to 17 years (N = 152) with a positive blood alcohol concentration (BAC) by lab test or self-report were recruited in the ED and randomly assigned to receive either MI or standard care (SC). Both conditions resulted in reduced quantity of drinking during the 12-month follow-up, whereas alcohol-related negative consequences were relatively low and stayed low at follow-up. Adolescents who screened positive for problematic alcohol use at baseline reported significantly more improvement on 2 of 3 alcohol use outcomes (average number of drinking days per month and frequency of high-volume drinking) if they received MI compared with SC. We conclude that brief interventions are recommended for adolescents who present to an ED with an alcohol-related event and report preexisting problematic alcohol use.