We used a retrospective cohort study design. First, using codes from the International Classification of Diseases, Ninth Revision (ICD-9), we identified all trauma patients hospitalized in 2006 to 2007 in Washington. Each patient's first hospitalization during these years was defined as their index hospitalization. We chose 2 comparison groups: a random sample of patients with a non–injury-related index hospitalization frequency matched with the injury group on age and year of hospitalization, and the general population of Washington. Information on outcomes was collected through 31 December 2011. The Human Subject Division of the Washington State Department of Health approved the study protocol and procedures.