The movement towards trauma care regionalization in Québec was initiated in 1990, with formal designation of three level I trauma centers in 1993. The purpose of this study is to evaluate the impact of trauma center designation on mortality. The study design is that of a two-cohort study, one assembled during 1987 when designation was not in effect, and the other during the first 5 months of designation. The study focuses on patients that fulfilled the following criteria: i) arrived alive at the hospital, and ii) were admitted. The outcome measures are adjusted mortality, and excess mortality as measured by the TRISS methodology. A total of 158 patients treated in 1987, and 288 treated in 1993, were identified. The mean age of the patients treated in 1993 was significantly higher (40.0, +/- 18.1), when compared with the 1987 group (30.9 +/- 18.1; p < 0.001). Patients in the 1987 cohort had a significantly higher proportion of injuries caused by stabbing (p = 0.02), and a significantly lower proportion caused by falls (p = 0.003). The 1987 cohort had a higher rate of abdominal injuries (p = 0.0001), and external injuries (p = 0.0001), and a significantly lower rate of head or neck injuries (p = 0.003), and injuries to the extremities (p = 0.0001). The mean Injury Severity Score (ISS) for the 1987 cohort was 14.96 (+/- 12.36), and 15.49 (+/- 11.61) in 1993 (p = 0.65). The crude mortality rate was 20% for 1987, and 10% for 1993. The crude odds ratio for mortality in 1987 was 2.10 with 95% confidence intervals between 1.22 and 3.62 (p = 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)