Objectives: The public health implications of regional variation in incidence and outcome of severe traumatic injury remain to be analyzed. The objective of this study was to determine whether the incidence and outcome associated with severe traumatic injury differs across geographic regions of North America. Methods: A prospective, observational study was conducted of the Resuscitation Outcomes Consortium of all patients in 9 North American sites (6 US and 3 Canadian) sustaining severe traumatic injury from April 1, 2006 to March 31, 2007 followed to hospital discharge. Eligible patients were assessed by organized emergency medical services, and had field-based physiologic criteria including systolic blood pressure ≤90 mm Hg, Glasgow Coma Scale score ≤12, respiratory rate <10 or >29 per minute, advanced airway procedure, or traumatic death in the field. Census data were used to determine rates adjusted for age and sex. The main outcome measures were incidence rate, mortality rate, case fatality rate, and survival to discharge for patients sustaining severe traumatic injury assessed by EMS. Results: The total catchment population of 20.5 million yielded 7080 cases of severe traumatic injury. Median age was 36 years and 67% were male. The median incidence of EMS-assessed severe traumatic injury per 100,000 population across sites was 37.4 (interquartile range [IQR] = 24.6-69.6); survival ranged from 39.8% to 80.8%, with a median of 64.5% (IQR = 55.5-78.4). About 942 cases were pronounced dead at the scene and 5857 patients were transported to hospital; 4477 (63.2%) were discharged alive. The median incidence of severe trauma due to a blunt mechanism, transported to hospital, was 25.8 (IQR = 13.1-44.3); survival ranged from 52.6% to 87.3%, with a median of 78.0% (IQR = 68.4-83.5). The median incidence of severe penetrating trauma, transported to hospital, was 2.6 (IQR = 1.5-10.4); survival ranged from 37.5% to 84.7%, with a median of 67.5% (IQR = 54.1-75.9). All P values for differences across sites for incidence and survival were <0.001. Conclusions: In this study involving 9 geographic regions in North America, there were significant and important regional differences in severe traumatic injury, incidence, and outcome. These differences were sustained for patients with either isolated blunt or penetrating injury mechanisms. Copyright © 2010 by Lippincott Williams & Wilkins.