OBJECTIVE:To examine (a) ethnic differences in blood alcohol level (BAL) and preinjury chronic alcohol use (PI-ETOH) within a severe closed head injury (CHI) sample and (b) the main and interaction effects of BAL, PI-ETOH, and ethnicity on functional outcome following severe CHI. PARTICIPANTS:A total of 434 Hispanic, Anglo-Caucasian, and African-American individuals with severe CHI. DESIGN:Retrospective cohort study. SETTING:Consecutive admissions to a level 1 trauma center. MAIN MEASURES:After admission to the trauma center, BAL was collected for each patient. Additional information regarding PI-ETOH was collected in a subset of patients (N = 116). Functional outcome was measured using the Disability Rating Scale (DRS) at 6 months after injury. RESULTS:A one-way analysis of variance revealed ethnic differences in mean BAL. Hierarchical multiple regression indicated that BAL did not predict DRS outcomes after controlling for pertinent covariates. An interaction effect between PI-ETOH and ethnicity was observed, such that presence of chronic alcohol use predicted worse functional outcome for Anglo-Caucasians and African-Americans, but more favorable outcome for Hispanics. CONCLUSIONS:Ethnic differences in BALs within our severe traumatic brain injury sample mirrored ethnic drinking patterns observed in the general population, with Hispanics having the highest BALs. A paradoxical relationship between PI-ETOH and functional outcome was observed for Hispanics.