OBJECTIVES: The purposes of this study were to evaluate the relationship between body mass index (BMI) and postoperative complications and to determine the incidence of reoperation after surgical treatment of pelvic ring injuries. SETTING: Three Level I trauma centers. PATIENTS/PARTICIPANTS: A retrospective review of 184 consecutive surgically treated pelvic ring injuries (Orthopaedic Trauma Association 61) was performed. Two patients died in the initial postoperative period, and the remaining 182 patients were followed for a minimum of 3 months. MAIN OUTCOME MEASUREMENTS: Complications that were evaluated included wound infection and dehiscence, loss of reduction, iatrogenic nerve injury, deep venous thrombosis, pneumonia, and the development of decubitus ulcers. Body mass index was calculated for each patient, and a BMI greater than 30 kg/m considered to be obese as defined by the National Institutes of Health. RESULTS: There were 132 males and 50 females with an average age of 36.4 years (range, 14-83 years). There were 48 (26%) patients with a BMI over 30 kg/m. Complications occurred in 46 of 182 patients (25.3%) with 26 occurring in the 48 patients with BMI greater than 30 kg/m (54.2% complication rate) and 20 occurring in the 134 patients with BMI less than 30 kg/m (14.9% complication rate). Complications included 20 infections (four superficial wound dehiscence and 16 deep), 23 losses of reduction, five deep vein thromboses, three pulmonary embolus, three pneumonia, two decubitus ulcers, and three iatrogenic nerve injuries. Reoperation was required in 29 of 182 (15.9%) patients with 16 (8.8%) irrigation and debridement, and 17 (9.3%) refixation procedures. All wound complications occurred after open exposures. Open exposures were performed for the anterior pelvic ring in 143 of 182 (78.6%) patients, the posterior pelvic ring in 64 of 182 (35.2%) patients, and percutaneous treatment of the posterior pelvic ring was performed in 80 of 182 (44.0%) patients. Logistic regression modeling analyzing BMI as a continuous variable found a relationship between increasing BMI and complication rate (P < 0.0001) and need for reoperation (P = 0.0013). Odds ratios analysis revealed that obese patients (BMI greater than 30 kg/m) were 6.87 (95% confidence interval, 3.25-14.49) times more likely to have a complication and 4.68 (95% confidence interval, 2.03-10.76) times more likely to undergo reoperation than patients with BMI less than 30 kg/m. CONCLUSIONS: Body mass index correlates with an increased rate of complications and reoperation after operative treatment of pelvic ring injuries.