Purpose:The purpose of our study was to investigate whether a simple scoring system based on the red blood cell distribution width (RDW), delta neutrophil index (DNI), and platelet count was associated with the prognosis of patients with sepsis, and whether this scoring system was more useful than each individual parameter.Materials and Methods:We conducted a retrospective cohort study involving adult patients who received intensive therapy due to severe sepsis and septic shock from January 2010 to December 2015 at a tertiary teaching hospital in South Korea.Results:A total of 730 patients were included in this study. Each patient was rated on a scale of 0 to 3 according to the new scoring system using the platelet count, RDW, and DNI. Point values were assigned based on the following definitions: RDW > 14.5%, DNI > 5.0%, and platelet count < 150 000/mm³. The 28-day mortality rate was 12.6% (92/730). The nonsurvivors had higher scores than the survivors (2.05 ± 0.80 vs 1.06 ± 0.87, P < .001). In the multivariate Cox proportional hazard analysis, the scoring system was an independent predictor of the 28-day mortality. The scoring system was well calibrated ( P = .81 for the goodness-of-fit test) and discriminated (area under the receiver operating characteristic curve = 0.785).Conclusion:Our new scoring system using the RDW, DNI, and platelet count was useful for predicting the mortality in patients with severe sepsis and septic shock.