BACKGROUND: Blunt thoracic aortic injury (BAI) is a rare and highly lethal injury. We sought to identify occupant and collision characteristics associated with motor vehicle collision (MVC)-related BAI. METHODS: The 1995 to 2000 National Automotive Sampling System data files were used. The National Automotive Sampling System is a national probability sample of passenger vehicles involved in police-reported tow-away MVCs. The risk of BAI was calculated according to specific occupant (e.g., age, seat belt use) and collision (e.g., delta-V [estimated change in velocity], vehicular intrusion) characteristics. The association between BAI and these characteristics was calculated using risk ratios (RRs) and associated 95% confidence intervals (CIs). RESULTS: Specific occupant and collision characteristics demonstrated independent association with BAI. Occupant characteristics included age >or= 60 (RR, 3.6; 95% CI, 2.5-5.2), seat belt use (RR, 0.3; 95% CI, 0.2-0.5), and being a front-seat occupant (RR, 3.1; 95% CI, 1.5-6.3). Frontal and near-side MVCs were associated with an increased risk (RR, 3.1; 95% CI, 1.9-5.1; and RR, 4.3; 95% CI, 2.6-7.2, respectively) relative to other collision types. Collisions with a delta-V >or= 40 km/h (RR, 3.8; 95% CI, 2.6-5.6) or that produce extensive vehicle crush (>or= 40 cm) (RR, 4.1; 95% CI, 2.7-6.3) or intrusion (>or= 15 cm) (RR, 5.0; 95% CI, 3.5-7.3) also increase the risk of BAI. CONCLUSION: The risk factors for BAI identified in this study support generally accepted etiologic mechanisms for this injury.