Objective: This study aims to assess the effect of obesity on injury severity score (ISS), mortality and course of hospital stay among trauma patients. Method: A systematic review of the literature was conducted by Internet search. Data were extracted from included studies and analysed using a random-effects model to compare outcomes in the obese (body mass index (BMI) >= 30 kg m(-2)) with the non-obese (BMI < 30 kg m(-2)) group. Result: Eventually, 18 studies met our inclusion criteria with 7751 obese patients representing 17% of the pooled study population. The data revealed that obesity was associated with increased risk of mortality, longer stay in the intensive care unit and higher rates of complication. Additionally, obese patients seemed to have longer duration of mechanical ventilation and hospital length of stay but it did not reach statistical significance. No difference was observed in ISS between the two groups. Conclusion: Evidence strongly supports the correlation of obesity with worse prognosis in trauma patients and further studies should target this kind of population for therapy and prevention. (C) 2012 Elsevier Ltd. All rights reserved.