ABSTRACT. Objective: Brief interventions in the emergency department targeting risk-taking youth show promise to reduce alcohol-related injury. This study models the cost-effectiveness of a motivational interviewing-based intervention relative to brief advice to stop alcoholrelated risk behaviors (standard care). Average cost-effectiveness ratios were compared between conditions. In addition, a cost-utility analysis examined the incremental cost of motivational interviewing per qualityadjusted life year gained. Method: Microcosting methods were used to estimate marginal costs of motivational interviewing and standard care as well as two methods of patient screening: standard emergencydepartment staff questioning and proactive outreach by counseling staff. Average cost-effectiveness ratios were computed for drinking and driving, injuries, vehicular citations, and negative social consequences. Using estimates of the marginal effect of motivational interviewing in reducing drinking and driving, estimates of traffic fatality risk from drinking-and-driving youth, and national life tables, the societal costs per quality-adjusted life year saved by motivational interviewing relative to standard care were also estimated. Alcohol-attributable traffic fatality risks were estimated using national databases. Results: Intervention costs per participant were $81 for standard care, $170 for motivational interviewing with standard screening, and $173 for motivational interviewing with proactive screening. The cost-effectiveness ratios for motivational interviewing were more favorable than standard care across all study outcomes and better for men than women. The societal cost per quality-adjusted life year of motivational interviewing was $8,795. Sensitivity analyses indicated that results were robust in terms of variability in parameter estimates. Conclusions: This brief intervention represents a good societal investment compared with other commonly adopted medical interventions. (J. Stud. Alcohol Drugs, 71, 384-394, 2010) Medicine, 1990;Maio et al., 1994). Drinking and driving is a particular problem (Miller et al., 1998), with approximately 25% of 18-to 19-year-old drivers involved in fatal auto accidents having a positive blood alcohol concentration (Subramanian, 2003).Reaching at-risk youth and designing effective interventions for alcohol-related problems is critical. One evidence-based approach is to intervene with youth receiving emergency medical treatment for an alcohol-related injury. Monti et al. (1999Monti et al. ( , 2007 and Spirito et al. (2004) have established that brief interventions conducted with adolescents in an emergency department (ED) reduce subsequent injuries and driving after drinking. Studies with older populations have also shown that ED interventions for problem alcohol use are efficacious in reducing alcohol-related consequences (Gentilello et al., 1999;Helmkamp et al., 2003;Longabaugh et al., 2001). In fact, the American College of Surgeons has mandated as a criterion for accreditation tha...