Abstract: Objective: To explore the association of red cell distribution width(RDM) with acute physiology and chronic health evaluation Ⅱ(APACHE Ⅱ) score,sequential organ failure assessment(SOFA) score,and prognosis of pneumonia patients complicated with septic shock.Methods: According to the case-control study,the clinical data in 86 pneumonia patients complicated with septic shock were retrospectively analyzed,and divided into the survival group(n=50) and death group(n=36) according to the 28-day prognosis.The RDW,white blood cell(WBC) count,hemoglobin(Hb),platelet(PLT) count,hematokrit(HCT) and platelet distribution width(PDW) were detected on admission,and the APACHE Ⅱ score and SOFA score in two groups were assessed.The relationship between RDW and other indexes,and disease severity and prognosis were evaluated.Results: The RDW in death group was significantly higher than that in survival group(P<0.01),the levels of Hb and HCT in death group were significantly lower than those in survival group(P<0.01),the differences of WBC,PLT and PDW between two groups were not statistical significance(P>0.05),and the scores of APACHE Ⅱ and SOFA in death group were significantly higher than those in survival group(P<0.01).Logistic regression analysis showed that the SOFA score(OR=1.282,95%CI 1.012-1.625,P<0.05) and RDW(OR=2.986,95%CI 1.661-5.368,P<0.01) were the independent risk factors of the death in pneumonia patients complicated with septic shock.The best cut-off value of RDW predicting the death risk of pneumonia patients complicated with septic shock was 15.05%(95%CI 0.767-0.948,P<0.01).Conclusions: RDW can be a clinical index in predicting the prognosis of pneumonia patients complicated with septic shock.The RDM examination is simple and low cost,which can be act as a complementary index.