OBJECTIVES: To generate national estimates of the effect of injury severity and admitting facilities' trauma center designation on inpatient costs, length of stay (LOS), and probability of death in hospital admissions for traumatic injury in the US. METHODS: Discharge data from the 2002 HCUP Nationwide Inpatient Sample were analyzed for 54,370 admissions (weighted N=267,306) to US trauma centers for blunt or penetrating traumatic injury. Data on admitting facilities' trauma center designation (Level I, II, or III/IV) were obtained from the American Hospital Association. For each admission, injury severity was calculated using the ICDMAP90 software. Regression analyses were used to estimate the incremental effect of injury severity and admitting facilities' trauma level on inpatient costs, LOS, and probability of death, controlling for injury type and other patient characteristics. RESULTS: Relative to critical injuries (ISS=25+), low severity (ISS=0-9), moderate severity (ISS=10-15) and severe (ISS=16-24) injuries were associated with substantially decreased costs (-$7467, -$6592, and -$5537, respectively; all P<0.0001), LOS (-9.7, -8.3, and -5.3 days, respectively; all P<0.0001), and probability of death (odds ratios = 0.032, 0.046, and 0.077, respectively; all P<0.0001). Relative to Level I trauma centers, Level II and Level III/IV centers were associated with lower costs (-$3407 [P=0.0051] and -$4454 [P<0.0001], respectively), LOS (-0.6 [P=0.0505] and -1.8 [P<0.0001] days, respectively), and probability of death (odds ratios = 0.818 [P=0.0090] and 0.732 [P=0.0515], respectively). CONCLUSION: To our knowledge, this is the first study to quantify the incremental effect of injury severity and admitting facilities' trauma center designation on inpatient costs, LOS, and probability of death in a representative multi-payer US population. Higher injury severity, as well as admission to more specialized trauma centers, was associated with increased costs, LOS, and probability of death. Results of this study may help healthcare decision makers more efficiently allocate resources for treatment of traumatic injuries.