The neutrophil-to-lymphocyte ratio (NLR) is an important predictive prognostic tool. However, its accuracy for predicting sepsis remains debatable. This study aimed to evaluate the factors influencing the ability of NLR to predict sepsis. Adult patients with sepsis or septic shock from the eICU database were enrolled in this study. Results showed that there was a significant difference in NLR between the survival and nonsurvival groups (median [lower quartile-upper quartile], 15.27 [7.92-26.28] vs. 17.97 [8.94-31.85], P = 0.008). Area under the curve (AUC) of NLR on the sixth day was the highest. AUC of NLR was significantly higher in the Simplified Acute Physiological Score (SAPS) 3 ≤52 group than that in the SAPS3 > 52 group (0.78 ± 0.05 vs. 0.69 ± 0.03, P = 0.007). AUC of NLR in the nonshock group was significantly higher than that in the shock group (0.72 ± 0.04 vs. 0.65 ± 0.05, P