['To determine whether morbidity and mortality were increased in morbidly obese patients who had reamed intramedullary nailing of closed femoral shaft fractures compared with similar patients of normal weight.', 'Retrospective case-control study.', 'Level I trauma center.', 'All patients with closed femoral shaft fractures treated with reamed intramedullary nailing over a 5-year period were identified. Normal-weight patients (BMI < 25) were compared with overweight (25 ≤ BMI < 30), obese (30 ≤ BMI < 40), and morbidly obese patients (BMI ≥ 40).', 'Reamed intramedullary nailing.', 'Occurrence of postoperative complications.', 'Of 507 patients with 526 femoral shaft fractures (AO/OTA-32), 184 (36.3%) were of normal weight, 170 (33.5%) were overweight, 114 (22.5%) were obese, and 39 (7.7%) were morbidly obese. There were no significant differences in complications when comparing normal-weight patients with overweight and obese patients. Systemic complications occurred in 23% of morbidly obese and 9% of normal-weight patients [odds ratio (OR) = 3.15, P = 0.013]. Morbid obesity increased odds of adult respiratory distress syndrome (OR = 35.38, P = 0.019) and sepsis (OR = 6.49, P = 0.0015). Overall, morbidly obese patients with a femoral fracture had a mortality rate of 10%, but a subset of polytraumatized patients (Injury Severity Score > 17) had a mortality rate of 20%. Morbid obesity significantly increased the odds of mortality (OR = 46.77, P = 0.01). Body mass index was found to be an independent predictor of adult respiratory distress syndrome, sepsis, and death.'] Does morbid obesity increase the risk for systemic complications in patients with femoral shaft fractures?