Objective To investigate the risk factors of polytrauma combined with multiple organ dysfunction syndrome (MODS).Methods A retrospective case control study was performed on the clinical data of 299 polytrauma patients admitted to the Affiliated Hospital of Jiangsu University from December 2011 to June 2017.The collected information included gender,age,length of hospital stay,number of injured parts,injury severity scores (ISS),neutrophil count,leukocyte level,hemoglobin level,platelet count,activated partial thromboplastin time (APTI),and D-dimer level within 24 hours since admission.In addition,shock within 24 hours since admission,infection after 3 days since admission,damage control surgery,underlying diseases and prognostic outcomes were also recorded.All the patients were divided into MODS group (94 patients) and non-MODS group (205 patients).Univariate and multivariate logistic regression analyses were used to determine the risk factors of polytrauma combined with MODS.Receiver operating characteristic (ROC) curve was applied to further analyze those risk factors identified by the former analyses.Results In the univariate analysis,there were statistically significant differences between the two groups in the number of injured parts,ISS,hemoglobin level,platelet count,APTT,D-dimer level within 24 hours since admission,shock within 24 hours since admission,infection after 3 days since admission,damage control surgery and prognostic outcomes (P ＜ 0.05).No significant differences were found in gender,age,underlying disease,length of hospital stay,neutrophil level,the leukocyte level within 24 hours since admission between the two groups (P ＞ 0.05).The multivariate logistic regression analysis showed that ISS (OR =1.048),shock within 24 hours since admission (OR =3.913),infection after 3 days since admission (OR =27.715),and D-dimer level within 24 hours since admission (OR =1.015) were significantly associated with polytrauma combined with MODS (P ＜ 0.05).In addition,the area under ROC curve of ISS was 0.726 (95 ％ CI 0.667-0.784),and the area under ROC curve of D-dimer was 0.638 (95％ CI 0.571-0.706).Conclusions The risk factors of polytrauma patients combined with MODS include ISS,infection after 3 days since admission,D-dimer level and shock within 24 hours since admission.In the treatment of polytrauma patients,attention should be paid to assessment of injury severity and coagulation function,active resuscitation to correct shock,prevent and control infection,which can reduce and prevent the risks for polytrauma patients combined with MODS.