In 2005, a major Level I trauma center closed in Los Angeles County, leading to media speculation that the sudden expansion of our catchment area would adversely affect outcome. We sought to determine whether the closure led to longer transport times and increased trauma morbidity and mortality at our Level I trauma center. Annual patient volume, paramedic transport times, injury severity score (ISS), mechanism of injury, complication rate, and mortality were retrospectively compared between two time periods, Period 1 (1997-2005, before closure) and Period 2 (March 1, 2005 to March 1, 2006, after closure), using multivariable logistic regression models. Median monthly patient volume rose from 123 patients to 190 patients in Period 2 (P < 0.01). Median transport time increased from 12 to 13 minutes (P = 0.004) and median ISS increased from four to five (P < 0.01) in Period 2. The proportion of patients with ISS > 15 increased from 17 to 24 per cent as well (P < 0.01). After accounting injury severity, the adjusted mortality rate decreased in Period 2 (odds ratio 0.69, P = 0.03) and the adjusted complication rate was unchanged (odds ratio 1.16, P = 0.2). In conclusion, the closure of a Level I trauma center resulted in a significant increase in trauma patient volume and injury severity, as well as a slight increase in paramedic transport times. However, the adjusted complication rate was unchanged, and the adjusted mortality rate actually improved.