Purpose: The delta neutrophil index (DNI) corresponds to the calculated immature granulocyte counts and the severity of sepsis. The aim of this study was to investigate the diagnostic value of DNI as a predictable laboratory marker for septic shock in patients with severe community-acquired pneumonia in emergency department. Methods: The present study was a retrospective analysis of patients with pathologically confirmed communityacquired pneumonia from December 2011 to February 2012 at a hospital. The DNI was automatically calculated as a subset of routine complete blood count test. The diagnostic performance of DNI for septic shock in patients with community-acquired pneumonia was evaluated. Results: During the study period, 105 patients were enrolled. Among them, 27 patients (25.7%) were confirmed as having septic shock according to predetermined criteria. The initial value of DNI was significantly higher in septic shock group than in non-shock group (8.7% vs 2.3%, p=0.008). The peak value of DNI was also significantly higher in septic shock group (18.6% vs 4%, p<0.001). The sensitivity and specificity of the initial and peak DNI values for predicting septic shock in patients with communityacquired pneumonia were 48.2%, 96.2%, 74.1%, and 87.2%, respectively, at initial and peak cutoff levels of 11.2% and 8.7% with an area under the curve (AUC) of 0.72 and 0.81 on the Receiver Operating Characteristic (ROC) curve. The AUC to predict septic shock was 0.74 for the CURB-65 scale. The AUC was significantly increased when peak DNI was added to CURB-65 scale (p=0.007). Conclusion: This study suggested that the DNI is associated with septic shock in patients with community-acquired pneumonia. Clinically, the peak value of DNI added to CURB-65 scale could improve predictable performance of septic shock in patients with community-acquired pneumonia.