Abstract Study objective The aim of this study was to investigate the prognostic prediction power of a newly introduced early warning score modified by serum lactate level, the National Early Warning Score–Lactate (NEWS-L) score, among community-acquired pneumonia (CAP) patients. We also compared the NEWS-L score with the pneumonia severity index (PSI) and CURB-65. Methods We designed a retrospective observational study and collected data on confirmed adult CAP patients who visited the study hospital between October 2013 and September 2014. Variables relevant to, the NEWS-L score, PSI, and CURB-65 were extracted from electronic medical records. Survival status at hospital discharge was determined in the same manner. The NEWS-L score was calculated as NEWS-L = NEWS + serum lactate level (mmol/L). The NEWS-L was divided into quartiles. The ability to predict mortality was assessed through area under the receiver operating characteristic curve analysis and calibration analysis. Results A total of 553 patients were enrolled, and the inpatient mortality rate was 10.8% (n = 60). Mortality rates increased incrementally in conjunction with the NEWS-L quartiles: first quartile, 2.2%; second quartile, 7.9%; third quartile, 9.6%; and fourth quartile, 23.9%. The area under the receiver operating characteristic curve of the NEWS-L score was 0.73 (95% confidence interval CI, 0.66-0.80), which showed no significant difference from that of the PSI (0.68; 95% CI, 0.61-0.76; P = .28) and CURB-65 (0.66; 95% CI, 0.59-0.73; P = .06). Conclusions The newly introduced early warning score modified by serum lactate level, NEWS-L score, was comparable to PSI and CURB-65, for predicting inpatient mortality among adult CAP patients.