BACKGROUND The American College of Surgeons delineates 108 requirements for level I trauma centers. Some of these requirements include: minimum of 1,200 trauma admissions per year; an average of 35 major trauma patients per surgeon; residency training programs; and 10 peer-reviewed journal submissions every three years. This study examines the variation in services provided among U.S. level I trauma centers. METHODS 218 facilities identified as level I trauma centers in 2005 were contacted for participation. 136 centers in 37 states completed the questionnaire. Surveys queried variances in trauma, neurosurgery, plastics, and orthopaedic surgery with regard to type of center, type of accreditation, number and training of participating physicians, number of beds, dedicated OR support (staff/rooms), call pay, and research. RESULTS Of the level I centers surveyed, 66% are university-affiliated facilities that employ more surgeons and staffing across trauma and all subspecialties compared to community-based or public centers. However, the community and public centers have more surgeons per capita (44% of the university-affiliated hospitals have six or more trauma surgeons on staff compared to 59% of the community and 70% of the public facilities). University-affiliated centers also provide more in-house subspecialty services (orthopaedic, neurosurgery, and plastics). Thirty-nine percent do not have ACS accreditation and are designated trauma facilities by state or local governments. Only 49% of trauma centers provide on-call pay to trauma surgeons, and these percentages decline for all subspecialties. Dedicated operating rooms and research programs are also lacking among all subspecialties. CONCLUSION Based on our findings, we conclude that there are no homogeneous criteria for being accredited as a level I trauma center. Reliable resources should be offered at any facility that claims a level I trauma designation. We do not know if such diversity of services truly impacts care or how it can be measured; nevertheless, it would be logical to presume that at some point services that fall below a minimum threshold would potentially adversely affect the quality of care. In order to develop appropriate policy to decrease possible disparities, differentiation in services between trauma centers must be further researched and described.