INTRODUCTION Major emergency abdominal surgery results in a high risk of morbidity and mortality. Preoperative neutrophil-to-lymphocyte ratio (NLR) has been proposed as a predictor of post-operative outcomes in elective surgery. The aim of the present study was to examine whether preoperative NLR was associated with post-operative morbidity and mortality after major emergency abdominal surgery. METHODS We conducted a retrospective cohort study of patients undergoing major emergency abdominal surgery in two university hospitals in Denmark between 2010 and 2016. Associations between preoperative NLR and 30-day post-operative complications and mortality were established through multivariate logistic regression and receiver-operating characteristics (ROC) analysis. RESULTS A total of 570 patients were included in the study. The overall 30-day mortality was 9.3% and 59.3% had post-operative complications. The median preoperative NLR was 8.6 (interquartile range: 4.8-14.7). Although NLR was higher in the group of patients who had complications or died after surgery, a multivariate analysis showed that the NLR was not associated with 30-day post-operative complications (odds ratio (OR) = 1.01 (95% confidence interval (CI): 0.99-1.02); p = 0.424) or mortality (OR = 0.99 (95% CI: 0.97-1.02); p = 0.57). The ROC analysis showed an area under the curve of 0.55 and 0.60 for 30-day post-operative complications and mortality, respectively. CONCLUSIONS Preoperative NLR was not associated with 30-day post-operative complications and mortality in patients undergoing major emergency abdominal surgery.  FUNDING none. TRIAL REGISTRATION not relevant.