BACKGROUND: A higher body mass index (BMI) is associated with hypoxia, hypercarbia, and reduced functional residual capacity. The current study evaluates the association between BMI and the need for mechanical ventilation (MV) among patients who have sustained chest trauma. METHODS: Demographic and clinical outcome data were collected from patients suffering blunt or penetrating thoracic traumatic injury admitted to a Level I academic trauma center between January 2001 and June 2006 (n = 3,649). Using logistic regression, the odds of being placed on MV were estimated according to BMI adjusting for the potentially confounding effects of age, mechanism of injury, severity of thoracic, head and overall injury, and pneumonia. RESULTS: Compared with those with a normal BMI (18.5-24.9 kg/m), the odds of MV were not significantly different for underweight (BMI < 18.5 kg/m) patients (odds ratio [OR] 0.98, 95% confidence interval [CI] 0.53-1.80), but were elevated for overweight (BMI 25.0-29.9 kg/m) and obese (BMI 30+ kg/m) patients (OR 1.40, 95% CI 1.08-1.81 and OR 1.53, 95% CI 1.17-1.99, respectively). CONCLUSIONS: Higher BMI values were positively associated with the initiation of MV. Among those patients on MV, an elevated BMI was significantly associated with a longer duration of MV. The field of acute trauma care would benefit from further evaluation of the association between BMI and MV so as to improve ventilation strategies for obese trauma patients. © 2007 Lippincott Williams & Wilkins, Inc.