Background: Alcohol screening and brief intervention (SBI) is used to decrease alcohol consumption, health care costs, and injury recidivism in trauma patients. Despite SBI being mandated for trauma centers, various concerns have led many centers to conduct SBI only on patients with a detectable blood alcohol concentration (BAC). We sought to determine the predictive nature of BAC on hazardous drinking behavior. Study Design: Adult trauma patients were included if they received an SBI before discharge. SBI was administered using a computerized alcohol screening and intervention (CASI) system with the Alcohol Use Disorder Identification Test (AUDIT). Data regarding demographics, injuries, and BAC were prospectively collected. Multivariate analyses were performed to identify independent predictors of hazardous drinking behavior. Results: Data were complete for 1,340 patients, with a mean age of 43 years (SD 20 years). Sixty-eight percent were male, 33% had detectable BAC, and 19% had hazardous drinking behavior. Multivariate analysis identified age (odds ratio [OR] 0.97 per year), male sex (OR 3.1), BAC (OR 1.009 per mg/dL), detectable BAC (OR 3.9), and legal intoxication (OR 7.8) as independent predictors of hazardous drinking behavior. Asian/Pacific Islander ethnicity was a significant negative predictor (OR 0.53) compared with white. Thirty-eight percent of patients with hazardous drinking behavior had no detectable BAC. Conclusions: Younger age, male sex, and higher BAC are early predictors of hazardous drinking behavior in adult trauma patients. Asian/Pacific Islander patients are half as likely to report hazardous drinking behavior compared with white patients. More than one-third of patients with hazardous drinking behavior do not have detectable BAC on admission and are not receiving interventions in centers that screen solely based on BAC. © 2012 American College of Surgeons.