Although obesity has been proposed as a risk factor for adverse outcomes after trauma, numerous studies report conflicting results. The objective of this study was to compare outcomes of obese and nonobese patients after trauma. The study population consisted of all trauma patients admitted to a surgical intensive care unit in a Level I trauma center from January 1999 to December 2002. Admission data, demographics, injury severity score (ISS), severity of illness, hospital course, complications, and outcomes were compared between obese (OB; body mass index [BMI] > or = 30), and nonobese patients (NOB; BMI < or = 29). A total of 918 patients was included in the study, 135 OB (14.7%) and 783 NOB (85.3%). There was no significant difference in demographic data, ISS, APACHE II score, and hospital stay. Intensive care unit stay was longer for OB patients (6.8 vs 4.8 days, P = 0.04). Overall mortality was 5.9 per cent for OB and 8.0 per cent for NOB patients (P = 0.48). Mortality by mechanism of injury was 3.4 per cent OB versus 7.4 per cent NOB (P = 0.26) for blunt and 10.6 per cent OB versus 10.2 per cent NOB (P = 0.9) for penetrating injury. The three most common complications associated with death were pulmonary, cardiovascular, and neurological deterioration. Using logistic regression analysis, age and ISS and APACHE II scores were associated with mortality, but BMI was not. We conclude that obesity does not appear to be a risk factor for adverse outcomes after blunt or penetrating trauma. Further research is warranted to uncover the reason for discrepant findings between centers.