ABSTRACT: BACKGROUND: Patient care may be inconsistent during off hours. We sought to determine whether victims of major trauma admitted to hospital on evenings, nights, and weekends suffer increased mortality rates. All victims of major trauma admitted to all four major acute care hospitals in the Calgary Health Region between April 1, 2002 and March 31, 2006 were included. Clinical and outcome information was obtained from regional databases. Weekends were defined as anytime Saturday or Sunday, evenings as 18:00-22:59, and nights as 23:00-07:59. RESULTS: Four thousand patients were included; 2,901 (73%) were male, the median age was 39.5 [inter-quartile range (IQR), 22.4-58.2] years, and the median injury severity score (ISS) was 20 (IQR, 16-26). Thirty-five percent (1,405) of patients were admitted on a weekend, 30% (1,197) during evenings, and 36% (1,422) at night. Seventy-eight percent (3,106) of cases presented during the "after hours" (evenings, nights, and/or weekends). The in-hospital case-fatality rate was 447 (11%), and was not significantly different during daytime (165/1,381; 37%), evening (128/1,197; 30%), and night (154/1,422; 36%) admissions (p = 0.53), or among patients admitted on weekends as compared to weekdays (157/1,405; 11% vs. 290/2,595; 11%; p = 1.0). Admission during the after hours as compared to business hours (343/3,106; 11% vs. 104/894; 12%; p = 0.63) did not increased risk. A multivariable logistic regression model was developed to assess factors associated with in-hospital death (n = 3,891). Neither admission on weekends nor on evenings or nights increased the risk for in-hospital mortality. CONCLUSION: In our region, the time of admission during the day or day of the week does not influence the risk for adverse outcome and may reflect our highly developed multi-hospital acute care and trauma system.